IGCSE Chemistry Paper-1: Specimen Questions with Answers 61 - 62 of 99

Question number: 61

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MCQ▾

Question

Which of the following allotrope of carbon is more reactive?

Choices

Choice (4)

a.

A and B of them are equally reactive

b.

Graphite

c.

Diamond

d.

A and B of them are non reactive.

Answer

b.

Explanation

In diamond, all the four valencies of each carbon atom are satisfied by bonding to other carbon atoms through regular covalent bonds. The electrons are held tightly between the nuclei, and there are no mobile electrons. Thus diamond structure is a closely packed structure and is extremely unreactive at room temperature.

In graphite, carbon atoms in each layer are bonded to three carbon atoms. This gives some double-bond character to C-C bonds giving it the presence of delocalized p-electron system. The layer-to-layer large distance makes graphite to have an open structure and so it reacts more readily.

Structure of Graphite

Structure of Graphite

Question number: 62

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MCQ▾

Question

Which of the following statements are true for unsaturated cyclic hydrocarbons?

i) Unsaturated cyclic hydrocarbons are those in which there is a single Carbon to carbon bond.

ii) Unsaturated hydrocarbons are those which do not contain more than six carbon atoms.

iii) Unsaturated hydrocarbons are called as aromatic compounds.

iv) None of these.

Choices

Choice (4)

a.

i) and iii)

b.

Only iv)

c.

Only iii)

d.

ii) and i)

Answer

c.

Explanation

The term ‘aromatic’ was assigned before the physical mechanism determining was discovered; the term was coined as such simply because many of the aromatic compounds have a sweet or pleasant odour.

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