Question

A hydrocarbon (A) has the molecular formula $\mathop C\nolimits_8 \mathop H\nolimits_{10}$. (A) is oxidised by a strong oxidising agent to (B). (B) on dehydration and subsequent reaction with ammonia forms an imide, (C). (C) is then reacted with a strong inorganic base to form a compound that undergoes Hoffman bromamide reaction to give (D). (D) is treated with sodium nitrite in an ice cold acidic solution to form the product (E). (E) is a steam volatile compound and on nitration gives two mononitro derivatives. (E) is treated with sodium hydroxide to form the salt (F). on heating a solution of (F), bubbles are formed due to release of gas. This gas does not burn. On analysis it was found that the gas has two components, one lighter than air and one heavier than air.

Compound B is :-
A.Phthalic acid
B.Isophthalic Acid
C.Terephthalic Acid
D.Benzoic acid

Answer 1

Degree of unsaturation in compound A)= $(2nC + 2) - \dfrac{{nH}}{2} = \left( {8 \times 2 + 2} \right) - \dfrac{{10}}{2} = {\text{ }}4^\circ$
Where nc is the number of carbon atoms and nH is the number of hydrogen atoms.
Degree of unsaturation is found here to know the ratio of carbon and hydrogen present in compound A.
This told that $C:H{\text{ }} = {\text{ }}1:1\;$so we can now know that compound A will be benzene with two extra carbons attached on it means to methyl group attached on it . As compound a is volatile to steam and when nitrated it gives nitro derivative so it will be now ortho-x

Complete step by step answer:
Phthalic acid :- when ortho-xylene is oxidised by the use of any oxidising agent both the methyl group in xylene will get converted to carboxylic acid and so formation of phthalic acid takes place. Hence this option is correct.
Isophthalic acid :- when ortho-xylene is oxidised the phthalic acid is formed as carboxylic group get attached on ortho positions but isophthalic acid has carboxyl groups on meta position . Hence this option is not correct.
Terephthalic acid :- it has a carboxylic group on para positions. But ortho-xylene when oxidised takes a carboxylic group on para positions. Hence this option is not correct.
Benzoic acid :- it has only one carboxyl group attached to it but xylene has two methyl groups and both of them get oxidised to carboxylic . So this option is not correct.

So, the correct answer is Option A .

Note:
When oxidation of ortho-xylene or naphthalene occurs then it leads to the formation of phthalic acid. When phthalic acid is heated it forms phthalic anhydride. When phthalic anhydride is treated with ammonia it forms phthalic imide (compound C).