Periodic Classification of Elements : Complete Set of Questions



This set of questions contains all the possible concepts
which could be asked in the examination

Earlier Attempts to classify Elements

Q.1 What was Dobereiner’s basis for classification of elements?

Dobereiner grouped the elements with similar chemical properties into three elements each called 'Triads'. The unique feature of a triad was the atomic mass of the middle element. When elements were arranged in order of their increasing atomic mass, the atomic mass of the middle element was approximately the arithmetic mean of the other two elements of the triad.


Q.2 What are the different triads that Dobereiner could identify?

Dobereiner's Triads are as follows:-


Q.3 What were the limitations of Dobereiner’s classification?

The major limitation of Dobereiner’s classification was that this was only applicable for some elements.

Only a limited number of elements could be arranged in triad form. 


Q.4 Write down Newlands’ law of octaves?

Newlands’ law of octaves state, “When the elements are arranged in the order of increasing atomic weights, then every eighth element has properties similar to that of the first element”

For e.g., if we start from lithium and arrange elements in ascending order of their atomic masses, the eighth element will be sodium.Both elements shows similar physical and chemical properties.


Q.5 Newlands’ octaves do not contain inert gases. Give reason?               

The inert gases were not known at that time and werediscovered later. Hence, they were not present in Newlands’ octaves.


Q.6 What were the limitations of Newlands’ law octaves?

The limitations of Newland‘s law of octaves are as follows:-

- Similarity in properties of elements as per the law was seen only up to calcium.

- At many places , two elements were put together at the same place.eg Co and Ni

- Fe having property similar to Co and Ni, was placed very far from them.

- All the elements discovered that time could not be classified into octaves.


Q.7  Up to which element, the law of octaves was found to be applicable?

The law of octaves was found applicable only up to calcium.

 

Mendeleev Periodic Table

Q.8 Define Mendeleev’s periodic law.

Mendeleev’s periodic law states, “The physical and chemical properties of the elements are the periodic function of their atomic masses”.


Q.9 In Mendeleev’s periodic law, what was the basis of the arrangement of elements?

Mendeleev’s periodic table was compiled on the basis of arranging the elements in increasing order of atomic masses and grouping them by similarity of properties.


Q.10 What were those two factors which Mendleev used for classification of elements?

Mendeleev used following two factors:-

(i) Increasing atomic masses

(ii) Grouping of similar elements together on the basis of their hydrides and oxides.


Q.11 List the achievements of Mendeleev’s periodic table.

The achievements of Mendeleev’s periodic table are as follows:-

• He classified all the 63 elements discovered at that time on the basis of similarities in properties.

• He left some gaps in periodic table for some elements which would yet to be discovered.

• He predicted the properties of some undiscovered elements which helped in the discovery of new elements.

• This classification helped to correct atomic weight of some elements on the basis of their position in the periodic table.


Q.12 What are the major drawbacks of Mendeleev’s classification?

Major drawbacks found in Mendeleev’s periodic table are as follows:

• Isotopes were placed together by Mendeleev as they have similar chemical properties but then this violated the arrangement scheme of increasing atomic mass.

• Position of hydrogen was uncertain in Mendeleev’s periodic table. Properties of hydrogen are similar to group 1 as well as group7 but Mendeleev placed it in group 1 without any proper explanation.

• The atomic mass in periodic table does not increase regularly. At some locations, elements were put in decreasing order of their atomic mass.eg.cobalt (58.93) preceded nickel (58.71) and tellurium (127.6) preceded iodine (126.7).


Q.13 Why did Mendeleev use oxides and hydrides of element as the basic properties of elements for their classification?

Mendeleev compared the chemical properties of elements by comparing their compounds.He selected hydrogen and oxygen as they are very reactive and formed compounds with most of elements. Hence he used oxides and hydrides of elements as the basic properties of elements for their classification.


Q.14 What are the elements which have been discovered that were left in Mendeleev‘s periodic table?

The elements discovered later are as follows:


Q.15 Give a detail account on properties of groups studied by Mendleev.

Mendeleev compared properties of groups by comparing their compounds. He selected oxides and hydrides of elements as the basic properties of elements for their classification.He found that most of the elements react with oxygen and hydrogen to form oxides and hydrides. From the chemical formula of oxides and hydrides of elements , he could classify the groups with similar properties. Formation of chemical compounds (oxides and hydrides) is as follows:-

(a) Formation of oxides: Any chemical coumpound in which the element is bonded with oxygen is known as oxide. If R is an element, then its oxide can be RO, R2O and R2O3

For e.g.

1. Li2O , Na2O and K2O resembles to R2

2. MgO, CaO, ZnO resembles to RO.

3. Al2O3 and B2O3 resembles to R2O3

(b) Formation of hydrides: Any chemical compound in which element is bonded with hydrogen is  known as hydride. If R is an element then its hydrides can be RH, RH2, RH3 and RH4

For e.g.


Q.16 What was the reason behind leaving some gaps in Mendeleev’s periodic table?

Mendeleev left some gaps in the periodic table for those elements which were not discovered at that time. He predicted that these elements would be discovered in future. He even predicted the properties of these elements in a group and surprisingly when these elements were discovered , his predictions were found correct


Q.17  Compare the properties of predicted and later discovered elements by Mendleev.

Gallium and germanium were not known at that time but Mendeleev named these elements by prefixing a Sanskrit word eka (meaning first) to the name of the preceding element in the same group.For eg eka-aluminium (first element after aluminium) for gallium and eka-silicon (first element after silicon) for germanium. Later on, these elements were discovered and Mendeleev’s predictions were found to be remarkably correct.


Q.18 In Mendeleev’s periodic table cobalt (atomicmass 58.93u) was placed before nickel (atomic mass of 58.71 u) .Give reason.          

Mendleev’s periodic table was based on increasing atomic mass but at some places he gave priority to similar chemical properties and arranged elements with higher atomic mass before lower atomic mass. Therefore, cobalt was placed before nickel.


Q.19 Write the formulae of chlorides of Eka- silicon and Eka-aluminium, predicted by Mendeleev.        

Mendeleev predicted germanium as Eka-silicon and gallium as Eka-aluminium.The formula of the chlorides are as follows:-

Modern Periodic Table

Q.20 Why are the elements chlorine, bromine and iodine called halogens?

 These elements are called halogens because they react with metals to form salts (Greek : halo = salt, gen = producer).


Q.21 Why are the elements calcium, strontium and barium named as alkaline earths?

These elements are called alkali metals because they react with water to form alkalis (caustic solutions). For example,


Q.22 How could the modern periodic table overcome different anomalies of Mendeleev’s periodic table?

Modern periodic table removes various anomalies of Mendeleev’s periodic table as follows:

(1) Position of Isotopes: Isotopes are placed together by Mendeleev as they have similar properties. But then this violated the arrangement scheme of increasing atomic masses. Modern periodic table use atomic number for arrangement of element. Atomic numbers of isotopes are similar so they should be placed at the same location in the periodic table.

(2) Anomalous pairs of elements: In Mendeleev’s periodic table, elements were put in order of decreasing atomic mass at some locations. For example Co and Ni. This was not explained by Mendeleev. As modern periodic table used atomic number for arrangement and Ni has higher atomic number, so it should follow Co in periodic table.

(3) Position of hydrogen: Mendeleev placed hydrogen in group 1 without any explanation in group 1.Later electronic configuration of hydrogen matches with electronic configuration of other elements of group 1. So it is placed in group 1.


Q.23 How many groups and periods are there in the modern periodic table?

There are 18 groups/ vertical columns and 7 periods/ horizontal rows in the periodic table.


Q.24 How many elements are present in modern periodic table?

There are 115 elements present in modern periodic table.


Q.25 What is atomic number? Why is atomic number used for arrangement of elements in a periodic table?

Atomic number is the number of protons present in nucleus of an atom. Physical and chemical properties of elements depend on number of electron which is equal to number of proton or atomic number. Thus, atomic number is a more suitable factor than atomic mass for arrangement of elements in a periodic table.


Q.26 What are  isotopes?

The term isotope is formed from the Greek roots iso ( "equal") and topos ("place"), meaning "the same place".Isotopes of an element have same atomic number and electronic configuration but different atomic mass.


Q.27 What are the different isotopes of hydrogen.      

Hydrogen has three naturally occurring isotopes.


Q.28 Isotopes of an element having different atomic masses share same position in the modern periodic table. Give reason.

Modern periodic table is based on atomic number. Since, all isotopes of an element have similar number of protons and hence same atomic number so placed at same position in modern periodic table.


Q.29 Define zero group elements.

The group of noble gases/ inert gases  i.e. He, Ne, Ar, Kr, Xe and Rn is called zero group because their valency is zero.


Q.30 Why zero group elements are chemically inactive?

The elements in zero group have a completely filled outer electronic shell and hence, have no tendency to lose, gain or share electrons. Thus, the elements in the group are chemically inactive.


Q.31 Give reason behind the late discovery of noble gases.

Noble gases are very inert / inactive. They are present in very low concentrations in our atmosphere hence discovered later.


Q.32 How many elements are present in lanthanoid family? What are their atomic numbers?

There are 14 elements present in lanthanoid family with atomic number, 58 – 71.


Q.33 What are actinoides?

The series having atomic numbers 90-103 are collectively known as actinoids. All the actinoids are radioactive.


Q.34 What are rare earth elements?

Lanthanoids are known as rare earth elements as they occur scarcely in the earth’s crust.


Q.35 What are alkali metals?

Group 1 in periodic table is known as alkali metals as these elements form alkaline solutions.


Q.36 What are alkaline earth metals?

Group 2 in periodic table is known as alkaline earth metals as they form alkaline solutions and their oxides melt at high temperature that they remain solids like earth in fires.


Q.37 Which group is known as pnicogens?

Group 15 or nitrogen family is also known as pnicogens which means “producing suffocation”


Q.38 What are chalcogens?

Group 16 or oxygen family is also known as chalcogens as they produces “ores”


Q.39 What are transition elements?

Elements of Groups 3-12 are knows as transition elements because they possess properties in between of group 1, 2 on left hand side and groups 13-18 on the right hand side in the periodic table.


Q.40 What are inner transition elements?

Both lanthanoids and actinoids are knows as inner transition elements because they form a series in between transition elements.


Q.41 Why silicon forms covalent bond?

Silicon has 4 electrons in the outermost shell so it can acquire nearest noble gas (Ar) configuration by losing , gaining or sharing 4 electrons.Because it takes lot of energy to lose or gain 4 electrons , Hence Si prefers to share its 4 electrons and forms covalent bond to get stable configuration.


Q.42 Why hydrogen is placed separately in periodic table?

Hydrogen is placed separately in the modern periodic table because of the following reasons :

(i) Hydrogen and alkali metals have similar outer electronic configuration (both have one electron in the valence shell). Therefore, some of the properties of hydrogen are similar to those of alkali metals and hence it can be placed in group 1 along with alkali metals.

(ii) Hydrogen and halogens have similar outer electronic configuration (both have one electron less than the nearest inert gas configuration). Therefore, some of the properties of hydrogen are similar to those of halogens and hence it can be placed in group 17 along with halogens.

(iii) In some properties, it differs from both hydrogen and halogens. For example, the oxide of hydrogen, i.e., H2O is neutral but the oxides of alkali metals (i.e., Na2O, K2O, etc.) are basic while those of halogens (i.e., Cl2O7 , Br2O5, I2O5, etc.) are acidic.

Hence, Hydrogen has a unique position in modern periodic table.

 

Periodic Properties

Q.43 Explain why the number of elements in the third period is 8?  

According to the 2 n2 rule, maximum number of electrons in the third period should be = 2 × 32 = 18

But the last shell cannot accommodate more than 8 electrons. Therefore, the number of elements in the third period is 8.


Q.44 Is it possible to have an element with atomic number 2.5 placed between helium and lithium?

No, because the atomic numbers of elements are always in whole numbers.


Q.45 Name the most metallic and  most non-metallic element in the Periodic Table.

The most metallic element is francium (group 1) and most non-metallic element is fluorine (group 17).


Q.46 What was the need for classification of elements?

As many as 115 elements are known today. It is quite difficult to study the properties of all these elements and millions of their compounds. This necessity led to the classification of various elements into different groups and periods.


Q.47 Which elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 13 respectively belong to the same period ?          

Electronic configuration of the given elements is as follows:-

B, C, D have two shells so they belong to same period i.e.2nd period


Q.48 Which is the outermost shell for elements of period 3? 

Periods shows the number of the outermost shell of any element.Since elements of period 3 occupies three shells hence outermost shell will be M.


Q.49 Which of the following elements does not lose an electron easily Na, F, Mg, Al?      

Na, Mg and Al are metals having tendency to lose electrons where as F is non metal having tendency to gain electron.So, F will not lose electron easily.


Q.50 Which of the following trends does not increase while moving down the group of the periodic table?           

Atomic radius, Metallic character, Valency, Number of shells in an element

In a group, number of valence electrons remains the same. Hence, valency remains the same for all the elements of a group.


Q.51 Compare the radii of two elements X and Y. Give reason for your answer.

(i) X has 12 protons and 12 electorns.

(ii) Y has 12 protons and 10 electrons.

Here, X and Y both have same atomic number so they are same element.

Electronic configuration of X = 2, 8, 2

Electronic configuration of Y=  2, 8

Y is losing two electrons and X is gaining those electrons. Because Y has less number of shells so its atomic radii is less compare to X.


Q.52 How hydrogen is different from both alkali metals and halogens?

Hydrogen differs from alkali metals and halogens in nature of oxides.The oxide of hydrogen, i.e. H2O is neutral but oxides of alkali metals (Li2O, Na2O, K2O, etc.) are basic while those of halogens (Cl2O7, Br2O5, I2O5, etc.) are acidic.


Q.53 Magnesium is more reactive than aluminium.Why?

As we go from left to right in a period, atomic size decreases, so the tendency of the element to lose electrons also decreases. As a result, reactivity decreases. Thus, Mg is more reactive than Al.


Q.54 Argon has bigger radii than chlorine.Why?

Atomic radii decrease along a period, therefore, atomic radius of Ar should be smaller than that of Cl. However, noble gases are inert and do not form diatomic molecules (i.e., Ar2) and hence have van der waals radii. On the other hand, Cl forms Cl2 and has covalent radius.Because van der Waals radii are bigger than covalent radii, therefore, atomic radius of argon is bigger than chlorine.


Q.55 What changes we observe in atomic size as we move down in a group?

On moving down the group, the number of shells increases.Each new shell is far from the nucleus from last shell hence, the distance between the nucleus and valence electron increases. Thus, atomic size also increases.

For eg if we move down in first group then atomic size will be change as follows:-

H < Li < Na < K < Rb < Cs


Q.56 What change in atomic size is observed on moving from left to right in a period in the periodic table?

On moving across a period, number of shells remains constant but effective nuclear charge increase which attracts valence electrons and hence atomic size decreases.

For eg if we move across in second period then atomic size will be change as follows:-

Li > Be > B> C > N > O > F


Q.57 Na (Sodium) atom is bigger than Li (Lithium) atom. Give reason.

'                                                                  K     L   M

Electronic configuration of Na atom = 2    8     1

Electronic configuration of Li  atom = 2     1

Number of shells are more in Na atom hence it is bigger than Li.


Q.58 Neon and argon are inert gases.

(i) What do their atoms have in common?

(ii) Why they do not take part in reactions?

(i) Neon and argon has completely filled valence shell so both are zero valent.

(ii) Neon and argonare zerovalentand hence, have no tendency to lose, gain or share electron. Thus, they are chemically inactive. 


Q.59 What are coinagemetals? Where they are placed in the periodic table?

Earlier, copper (Cu), silver (Ag) and gold (Au) were used for making coins and hence these metals are called coinage metals. They are placed in group 11 in the periodic table.


Q.60 Write down the major difference between Mendeleev’s periodic table and the modern periodic table.

The major differences between Mendeleev’s and Modern periodic table are as follows:-


Q.61 How does an atom relate its electronic configuration with its position in the Periodic Table?

In the Modern Periodic Table, there are 18 groups and 7 periods.The number of valence electrons shows the group number and number of valence shells denotes period number  in the periodic table.           

Relation between group number and period number with electronic configuration is as follows:-

Relation with group: For groups 1and 2 , the number of valence electrons is equal to the            group number but for groups 13-18, the number of valence electrons is equal to group    number minus 10.

Relation with period: Number of valence shell represents the number of period.

For eg if an element belongs to third period and group 15 ,  this indicates that it has 3 shells and number of valence electrons wil be group number – 10 = (15-10 ) = 5

So its electronic configuration will be

K          L          M

2          8          5

Conversely, if the electronic configuration is given, we can find its position in the periodic table. For example, if an element has following electronic configuration:-

K          L          M         N

2          8          18        5

Since the element has 5 valence electrons so its group number will be

Valence electrons= group number -10

5=group number -10

Group number = 10+5 = 15

Thus,  it belongs to group15. Since the valence shell is the 4th shell (i.e. N), therefore, the element lies in the 4th period. In other words the given element lies in group 15 of the 4th period.Thus, electronic configuration shows the position of the any element in the periodic table and vice-versa.


Q.62 What are the major drawbacks present in Modern periodic table?

The major drawbacks present in modern periodic table are as follows:-

• Position of hydrogen is still not proper in modern periodic table. As it has resemblance with alkali metals, it shows similarities with halogens aswell. So it can be placed in group 17 along with halogens. At the same time hydrogen differs from alkali metals as well as halogens in some aspects. Fore.g. hydrogen forms neutral oxide, alkali metals forms basic while halogen forms acidic oxides. Hence the position of hydrogen in controversial in modern periodic table as well.

• Position of helium is also controversial in modern periodic table. Helium should be placed in group second along with alkaline earth metals as it has 2 electrons in outermost shell but it is placed in group 18 with inert gases.

• Lanthanides and actinides have not been got proper place in modern periodic table. They placed separately in periodic table.


Q.63 How does metallic character changes along a period?

Metallic character tends to decreases along a period from left to right in periodic table. On moving across the period, the size of the atom decreases which results in increase in attraction on valence electrons and hence it become difficult to lose electron. So, metallic characters decreases.

For eg in third period Na, Mg, Al are metals,Si is a metalloid and P, S and Cl are non metals.

Na    Mg      Al             Si            P     S    Cl

(     Metallic   )       (Metalloid)    (Non metals)


Q.64 Element X forms a chloride with the formula XCl2. Find the position of the X in the periodic table.

The formula of the chloride, XCl2 suggests that the valency of X is 2, so it belongs to group second in the periodic table.


Q.65 If an element A belongs to group 14, write the formula and the nature of bond formed of its chloride?

Element ‘A’ belongs to group 14, hence , its valence is 14 – 10 = 4.Since it is not easy to either lose all the four valence electrons or gain four more electrons, therefore, it share these four electrons to get the  nearest noble gas stable electronic configuration.Thus, the nature of bond of its chloride is covalent.


Q.66 Which is an essentialconstituent found in all organic compounds and where it is placed in modern periodic table?

Carbon is an essential constituent of all organic compounds belong to group 14 and period 2nd.


Q.67 Out of Mg, Na, K, Ca which of the elements would lose an electron easily?  

Electronic configurations of different elements are as follows:-

From the above electronic configuration, it is clear that K and Na , both have one valence electronand hence  will lose an electron more easily compared to Mg and Ca with two electrons .In K and Na , K has more number of shells which results in less attraction between nucleus and valence electrons and easy to lose electron.


Q.68 Chlorine (atomic number 17) is more electronegative than sulphur (atomicnumber16).Give reason.

Electro negativity is a tendency to gain electron. As we move across period, size of atom decrease which results in more attraction power for coming electron and hence electro negativity also increases. Therefore, Cl is more electronegative than S.


Q.69 An element A is placed in 2nd group and 4th period and burns in the presence of oxygen to form a basic oxide.

(a) Identify the element.

(b) Write its electronic configuration.

(c) Write a balanced equation for the reaction when this oxide is dissolved in water.    

(a) Calcium(because it contains 4 shells and 2 valence electrons)

(b) Electronic configuration of Ca = K    L    M   N

'                                                               2     8    8    2

(c)


Q.70 The position of three elements A, B and C in the periodic table is given below :

                                             C

Answer the following questions.

(a) Out of B and C, which element will be more metallic?

(b) Out of C and A, which is bigger?

(c) Out of B and C, which will be more electronegative?

(a) On moving down in a group, size of atom increases results in less attraction power on valence electron and can lose electron easily.So, metallic characters increases hence C is more metallic than B.

(b) On moving across a period number of shells remains constant but effective nuclear charge increases hence atomic size decreases. So, C is smaller than A.

(c) Electro negativity is a tendency to gain eletrons.On moving down in a group atomic size increases which results in less attraction on coming electrons hence electro negativity decreases. So B will be more electronegative.


Q.71 An element belongs to 2nd group and 3rd period of the periodic table burns in the presence of oxygen to form a basic oxide.

(a) Name the element.

(b) Write down its electronic configuration.

(c) Write the balanced equation when it reacts with oxygen.

(d) Write down the balanced equation when this oxide reacts with water

(e) Draw the electron dot structure for the formation of this oxide.

(a) Magnesium (Because it contains 3 shells and 2 valence electrons)

(b) Atomic number of magnesium is 12, so electronic configuration is 2, 8, 2.

(c)

(d)

(e) Structure of MgO

Valency of Mg = +2

Valency of O   =  -2

Magnesium loses 2 electrons and oxygen accepts these 2 electrons and ionic bond will form.

Electron Dot Structure of MgO (Magnesium oxide)


Q.72 Write the formula of the product formed when the element A(atomic number 11) combines with the element B (atomic number 8).Draw its electron dot structure.What is the nature of the bond formed?

Electronic configuration of A and B are as follows:

K  L M

A (11) = 2   81

B (8) = 26

A has valency 1, B has valency 2

By crossing over valencies formula will be A2B and bond formed will be ionic in nature.

Here A is giving electron to B.


Q.73 Define the term electronegativity.

Electro negativity is a property of an atom to attract electrons towards itself.


Q.74 How electronegativity changes across the period and moving down in a group?

On moving across a period size of atom decreases which results in increase in effective nuclear charge so electro negativity of elements also increases. On moving down a group, size of atom increases hence electro negativity decreases.

For e.g. in third period electro negativity changes as follows:-

Na < Mg < AL < Si < P < S < Cl

In first group electro negativity changes as follows:-

Li> Na > K > Rb> Cs


Q.75 Define the term valency.

Valency is defined as a combining capacity of atoms with other atoms when they form compounds.


Q.76 How valency changes across the period and moving down in a group?

All the elements present in a group have the same outermost electronic configuration of their atoms. Hence, have the same valency.

On moving across a period, elements do not have the same number of valence electrons, hence they show different valencies.For group 1,2,13,14 valency is equal to its valence electron where as for group 15-18 , valency is equal to ( 8 - valence electron).

For eg. valencies of elements present in third period are as follows:

Elements         :           Na       Mg       Al         Si         P          S          Cl         Ar

No of valence e   :     1          2          3          4          5          6          7          8

Valency   :                   1         2          3           4      (8 – 5) (8 – 6)   (8 – 7) (8 – 8)

= 3       = 2       = 1       = 0


Q.77 What is atomic radius?

Atomic radius is a measure of size of atom of any element. It is a distance between center of atom and the valence electron.


Q.78 How atomic radius changes across the period and moving down in a group?

On moving across a period, number of shells remains constant but effective nuclear charge increase which attracts valence electrons and hence atomic size decreases.

In a group as we move down, as number of shells increases, the distance between the center of the nucleus and valence electrons also increases therefore atomic size increases.


Q.79 What is ionization energy?

Ionization energy is a minimum amount of energy to remove an electron from an atom or molecule in gaseous state.


Q.80 How ionization energy changes across the period and moving down in a group?

Moving across a period, size of atom decreases so effective nuclear charge on valence electrons increases so it takes more energy to remove a valence electron hence ionization energy increases.

On moving down in a group, size of atom and number of shells increases which results in decreased effective nuclear charge so it becomes easy to remove valence electrons hence ionization energy decreases.


Q.81 What is electron affinity?

Electron affinity is an amount of energy released when an electron is added to an atom in its gaseous state.


Q.82 How electron affinity changes across the period and moving down in a group?

Moving across a period, size of atom decreases and effective nuclear charge increases which results in increase in tendency to gain an electron hence electron affinity also increases.

On moving down in a group, size of atom increases which results in decreased effective nuclear charge for coming electron hence electron affinity also decreases.


Q.83 How nature of oxidesof changes across the period and moving down in a group?

Metals form basic oxides where as non metals form acidic or neutral oxides. When we move from left to right in a period, non metallic characters increases hence acidic nature of oxides increases. Similarly, on moving down the group, as metallic character increases, it also causes an increase in basic nature of oxide.


Q.84 Properties of the elements are given below.Identify the elements which is

(a) A soft metal stored under kerosene.         

(b) An element with variable valency stored under water.

(c) An element which is tetravalent and forms the basis of organic compounds.

(d) An element which is an inert gas with atomic number 2.

(e) An element whose thin oxide layer is used to make other elements corrosion resistant by the process of ‘anodising”.

(a) Alkali metals or group 1 are soft and reactive towards air and moisture and hence are stored under kerosene. For example, Na, K etc.

(b) Phosphorus shows variable valency of 3 and 5. It is reactive towards air and not towards water. Therefore, it is stored under water.

(c) The element carbon is tetravalent and is the basis of organic compounds.

(d) The inert gas with atomic number 2 is helium (He).

(e) The metal whose thin oxide layer (i.e., Al2O3) is used to make other metals corrosion resistant by the process of anodizing is aluminium (Al).

 

Value Based Questions : -

Q.1 A private company hasone senior manager teaching managing skills of 5 different departments. He is able to teach only few peoples of same department at a time. Some persons learn very fast and even help others as well.

(a) How will you compare the tendency to lose or gain electrons with the nature of different people?

(b)  Do you think is it possible to teach all departments together?

(c)  Which value is acquire by people who help others in learning new skills?

(a) People who share their knowledge and help others are same as donating electrons to give someone who need and those who receive knowledge are same as gaining electrons to fulfill their need.

(b) No, because people of all departments have different abilities therefore, should be taught separately.

(c) They have concern for others and believe in sharing. 


Q.2 Tanvi is a student of Class X. Her class teacher gave her an assignment to write a review on any of the books written by “BhishamSahni”. She goes to the library but was unable to locate anyone. She approaches the librarian for help. The librarian took her to one of the sections of the library and showed her many books of “BhishamSahni”. 

(a) How librarian help Tanvi to find the book easily?

(b) What are the two values Tanvi learnt?

(a) Librarian has arranged all books in orderly manner (as elements arranged in periodic table) and it make easy to find any book.

(b) Orderliness and knowledge of classification.



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