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Class 10 Science Chapter 4: Carbon and its Compounds MCQs with answers

10 multiple-choice questions on Carbon and its Compounds, each with its answer and the reason, written from the NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter.

Question 1
A student suggests that carbon could reach a noble gas configuration by losing all four of its valence electrons to form C⁴⁺. The main objection to this is that
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Answer: (a) removing four electrons would need a large amount of energy

Losing four electrons would need a large amount of energy, so C⁴⁺ does not form. Option b is the objection to C⁴⁻ (gaining four), not to C⁴⁺.

Question 2
In which of these molecules do the two atoms share the largest number of electrons between them?
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Answer: (b) N₂

H₂ and Cl₂ share one pair (2 electrons), O₂ shares two pairs (4 electrons), N₂ shares three pairs (6 electrons) in its triple bond.

Question 3
Candle wax, a mixture of carbon compounds, melts at about 330 K, while common salt melts only above 1000 K. The low melting point of wax is best explained by
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Answer: (b) weak forces between separate wax molecules, though the bonds within each molecule are strong

Covalent molecules have strong bonds within the molecule but only weak forces between molecules, so little energy separates them and they melt low. Wax has no ions, and it is made of C–H chains.

Question 4
A diamond in a ring and the graphite rod of a dry cell are both pure carbon. Which statement about the two is correct?
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Answer: (c) They have the same chemical properties but very different physical properties.

Diamond is the hardest substance while graphite is smooth, slippery and conducting, yet their chemical properties are the same. Only diamond has four bonds per carbon; graphite has three in a plane.

Question 5
A form of carbon whose molecule has sixty carbon atoms arranged like the panels of a football belongs to the class called
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Answer: (b) fullerenes

Fullerenes are a class of carbon allotropes; the first identified, C-60, has its atoms arranged in the shape of a football.

Question 6
Silicon, like carbon, has four valence electrons, yet it forms only a handful of compounds with hydrogen. The reason is that
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Answer: (c) silicon chains stop at about seven or eight atoms and those compounds are very reactive

Silicon's hydrogen compounds have chains of only up to seven or eight atoms and are very reactive; carbon's long, stable chains give it millions of compounds.

Question 7
An open-chain hydrocarbon has the molecular formula C₅H₁₀. It belongs to the
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Answer: (a) alkenes

C₅H₁₀ fits CₙH₂ₙ with n = 5, the general formula of alkenes. An alkane would be C₅H₁₂, an alkyne C₅H₈, and it has no oxygen.

Question 8
The first member of the alkyne series is ethyne. The molecular mass of the fourth member of the series is (C = 12 u, H = 1 u)
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Answer: (d) 68 u

Ethyne C₂H₂ = 26 u; each step adds –CH₂– (14 u): propyne 40 u, butyne 54 u, pentyne C₅H₈ = 68 u. 54 u is the third member, 70 u is C₅H₁₀, 82 u the fifth.

Question 9
Which of the following is a structural isomer of CH₃–CH₂–CH₂–CH₃?
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Answer: (c) CH₃–CH(CH₃)–CH₃

Isomers share the molecular formula but differ in structure. CH₃–CH(CH₃)–CH₃ is C₄H₁₀ with a branched chain. The others are C₃H₈, C₄H₈ and C₅H₁₂.

Question 10
Benzene and cyclohexane each contain a ring of six carbon atoms. Which statement is correct?
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Answer: (b) Benzene, C₆H₆, is unsaturated; cyclohexane, C₆H₁₂, is saturated.

Cyclohexane is C₆H₁₂ with single bonds only; benzene, C₆H₆, is a cyclic unsaturated hydrocarbon.

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