CBSE - Chemistry - Carbon and its Compounds

15. Pentane has the molecular formula C₅H₁₂. It has
(a) 5 covalent bonds
(b) 12 covalent bonds
(c) 16 covalent bonds
(d) 17 covalent bonds
Ans. (c) 16 covalent bonds
Explanation: Following is the structural formula of pentane. It shows 16 covalent bonds:


16. Structural formula of benzene is

Ans. (c)
Explanation: Formula of benzene is C6H6. Option (a) and (d) show the same formula. In option c, all the arms of carbon atoms are occupied.

17. Ethanol reacts with sodium and forms two products. These are
(a) sodium ethanoate and hydrogen
(b) sodium ethanoate and oxygen
(c) sodium ethoxide and hydrogen
(d) sodium ethoxide and oxygen
Ans. (c) Sodium ethoxide and hydrogen
Explanation: This reaction can be shown by following equation:

2Na + 2CH₃CH₂OH → 2CH₃CH₂ONa + H₂

18. The correct structural formula of butanoic acid is


Ans. (d)
Explanation: Formula of butanoic acid is C₃H₇COOH.

19. Vinegar is a solution of
(a) 50% - 60% acetic acid in alcohol
(b) 5% - 8% acetic acid in alcohol
(c) 5% - 8% acetic acid in water
(d) 50% - 60% acetic acid in water
Ans. (c) 5% - 8% acetic acid in water

20. Mineral acids are stronger acids than carboxylic acids because
(i) mineral acids are completely ionized
(ii) carboxylic acids are completely ionized
(iii) mineral acids are partially ionized
(iv) carboxylic acids are partially ionized
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)
Ans. (a) (i) and (iv)
Explanation: Mineral acids are completely ionized but carboxylic acids are partially ionized. Hence, mineral acids are stronger acids than carboxylic acids.

21. Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g. hydrogen. After the formation of four bonds, carbon attains the electronic configuration of
(a) helium
(b) neon
(c) argon
(d) krypton
Ans. (b) Neon
Explanation: Electronic configuration of carbon is 2, 4 and after sharing four electrons from four univalent atoms, its electronic configuration becomes 2, 8 which is same as that of Neon.


22. The correct electron dot structure of a water molecule is
(a) (b)  (c)  (d)


Ans. (c) Explanation: This dot structure shows a complete octet after oxygen shared two electrons with two univalent atoms of hydrogen.

23. Which of the following is not a straight chain hydrocarbon?


Ans. (d)
Explanation: In this option, three carbon atoms are sharing electrons with univalent atoms. In other options, only two carbon atoms are sharing electrons with univalent atoms.


24. Which among the following are unsaturated hydrocarbons?

(a) (i) and (iii)
(b) (ii) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)
Ans. (c) (ii) and (iv)
Explanation: These compounds show double and triple bonds. Hence they are unsaturated hydrocarbons

25. Which of the following does not belong to the same homologous series?
(a) CH₄
(b) C₂H₆
(c) C₃H₈
(d) C₄H₈
Ans. (d) C₄H₈

Explanation: The general formula for this compound is C_nH_2n, while that of other options is C_nH_2n+2.


26. The name of the compound CH₃— CH₂— CHO is
(a) Propanal
(b) Propanone
(c) Ethanol
(d) Ethanal
Ans. (b) Propanone
Explanation: This compound has −CHO as active radical. Hence, one suffix is used.


27. The heteroatoms present in CH₃— CH₂— O — CH₂— CH₂Cl are
(i) oxygen
(ii) carbon
(iii) hydrogen
(iv) chlorine
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
Ans. (d) (i) and (iv)
Explanation: Oxygen and chlorine are not among essential components of hydrocarbons.

28. Which of the following represents saponification reaction?


Ans. (d)
Explanation: When ester is treated with an alkali, the reaction gives ethanol and sodium ethanoate. This reaction is called saponification reaction.


29. The first member of alkyne homologous series is
(a) ethyne
(b) ethene
(c) propyne
(d) methane
Ans. (a) Ethyne