Assertion: Anisole on nitration gives ortho- and para- substituted products.

Reason: Ortho- and para- substituted products are obtained because it a nucleophilic substitution reaction.

Assertion is correct but the Reason is incorrect

The correct answer is option 3. Assertion is correct but the Reason is incorrect.

Assertion: Anisole on nitration gives ortho- and para- substituted products.

This statement is correct. When anisole (methoxybenzene) undergoes nitration with a mixture of concentrated \(HNO_3\) and \(H_2SO_4\), it forms a mixture of ortho-nitroanisole and para-nitroanisole isomers as the major products.

Reason: Ortho- and para- substituted products are obtained because it's a nucleophilic substitution reaction.

This statement is incorrect. Nitration of anisole is an example of an electrophilic aromatic substitution reaction, not a nucleophilic substitution reaction.

Explanation:

In electrophilic aromatic substitution, an electrophile (electron-loving species) attacks the aromatic ring, substituting one of the ring's hydrogens. In nitration, the electrophile is the nitronium ion \((NO_2^+)\) generated from the \(HNO_3/H_2SO_4\) mixture.

Nucleophilic substitution reactions, on the other hand, involve a nucleophile (electron-donating species) attacking a molecule and displacing a leaving group.

The reason why anisole preferentially undergoes nitration at the ortho and para positions is due to the directing effect of the methoxy group \((OCH_3)\) present in the molecule. The methoxy group is an electron-donating group, which activates the benzene ring and makes it more susceptible to electrophilic attack. Additionally, the methoxy group directs the incoming nitro group to the ortho and para positions through resonance effects.

The assertion is correct because nitration of anisole leads to ortho- and para-nitroanisole isomers. However, the reason provided is incorrect as the reaction is an electrophilic aromatic substitution, not a nucleophilic substitution.