X CBSE Science Ch. Carbon and its compound Solved Important questions

1.Q. Why carbon form covalent bond by sharing electron?

Ans: Carbon has four electrons in its outermost shell and needs to gain or lose four electrons to attain noble gas configuration.  (i) it could gain four electrons forming C^4- anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons. (ii) It could lose four electrons forming C⁴⁺ cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons.

Hence, it is difficult for the carbon to lose or gain four electrons therefore  carbon form covalent bond by sharing electron

2.Q. Why do covalent compounds are in gaseous or liquid state at normal temperature and pressure.

Ans: due to Weak Vanderwaal’s forces present between the molecules of covalent compounds.  

3.Q. Why do covalent compounds have less melting and boiling points?

Ans: As energy required breaking the crystal is less due to the presence of weak Vanderwaal’s force.

4.Q. Why do covalent compounds are bad conductors of electricity?

Ans: Due to the absence of free electrons or free ions.

5.Q. Why graphite has high melting point?

Ans: Within each layer of graphite, every carbon atom is joined to three others by strong covalent bonds. This forms a pattern of interlocking hexagonal rings. The carbon atoms are difficult to separate from one another. So graphite also has high melting point.

6.Q.why is  diamond known as the hardest metal?

Ans: each carbon is  linked to four other carbon atoms forming regular and tetrahedral arrangement and this network of carbon atoms extends in three dimensions and is very rigid. This strong bonding is the cause of its hardness and its high density.

7.Q.Define term  allotropy?

Ans: Allotropy is the property by virtue of which an element exist in more than one form and each form has different physical properties but identical chemical properties. These different forms are called allotropes. The two common allotropic forms of carbon are diamond and graphite.

8. Which of the following is an allotropic form of carbon ?

(A) Diamond                                         (B) Graphite             
 (C) Fullerene                                        (D) All of these         Ans: D

9 . Diamond is not a good conductor of electricity because -

(A) it is very hard.                                 (B) its structure is very compact.

(C) it is not water soluble.                      (D) is has no free electrons to conduct electric current.         
 Ans: D

10.. In a double covalent bond number of electron pairs shared are -

(A) 2                                                   (B) 3

 (C) 4                                                  (D) 6                          Ans: A

11. Which of the following compound contain single covalent bond ?

(A) Oxygen                                          (B) Nitrogen

(C) Methane                                        (D) Carbon dioxide      Ans: C

12. Carbon dioxide molecule contains -

(A) single covalent bond                        (B) double covalent bond

(C) triple covalent bond                         (D) ionic bond            Ans: B

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