Question

Phenol, when it first reacts with concentrated sulphuric acid and then with concentrated nitric acid, gives
(A) 2,4,6-trinitrobenzene
(B) o-nitrophenol
(C) p-nitrophenol
(D) nitrobenzene

Answer 1

The -OH group attached to the benzene ring in phenol has the effect of making the ring much more reactive than it would otherwise be. It also reacts with dilute nitric acid, whereas benzene itself needs a nitrating mixture of concentrated nitric acid and concentrated sulfuric acid.

Complete answer:
We have been provided with phenol,
Phenol is an aromatic organic compound with the molecular formula ${{C}_ {6}} {{H}_ {5}} OH$,
When phenol reacts with concentrated sulphuric acid,

Phenol reacts with sulfuric acid giving substituted phenols. At room temperature an equilibrium is established between a mixture of phenol sulphuric acid and the product benzene ortho hydroxy sulfuric acid.
And then the product benzene ortho hydroxy sulfuric acid reacts with concentrated nitric acid,
Phenol on reaction with conc. ${{H}_ {2}} S{{O}_ {4}}$ gives a mixture of o- and p- products and then at room temperature o- product is more stable, which on treatment with conc. $HN{{O}_ {3}}$ will yield o-nitrophenol. Since temperature is not mentioned, o-nitrophenol is the only stable product.

When benzene ortho hydroxy sulfuric acid reacts with concentrated nitric acid ortho-nitrophenol is formed.

Therefore, we can conclude that option (B) is correct.

Note:
Ortho-nitrophenol is stabilized by intramolecular Hydrogen-bonding between the H-atom of OH group and an oxygen of the nitro-group. Para-nitrophenol lacks such extra stability and hence, is relatively less stable than o-nitrophenol. Hence, the major product is o-nitrophenol.