The correct answer is A. naphthalene.
Naphthalene-1 sulphonic acid is a substituted naphthalene with a sulfonic acid group attached to the 1-position of the naphthalene ring. When heated with dilute sulfuric acid, the sulfonic acid group is deprotonated, leaving behind a positive charge on the naphthalene ring. This positive charge is then stabilized by resonance with the naphthalene ring, resulting in the formation of naphthalene.
Naphthalene-2-sulphonic acid is a different compound with the sulfonic acid group attached to the 2-position of the naphthalene ring. When heated with dilute sulfuric acid, the sulfonic acid group is deprotonated, leaving behind a positive charge on the naphthalene ring. However, this positive charge is not as stable as the positive charge on naphthalene-1 sulphonic acid, because it cannot be stabilized by resonance with the naphthalene ring. As a result, naphthalene-2-sulphonic acid is less likely to be formed than naphthalene.
1-naphthol and 2-naphthol are both derivatives of naphthalene with hydroxyl groups attached to the 1- and 2-positions of the naphthalene ring, respectively. When heated with dilute sulfuric acid, the hydroxyl groups are protonated, leaving behind negative charges on the naphthalene rings. These negative charges are not as stable as the positive charge on naphthalene, because they cannot be stabilized by resonance with the naphthalene ring. As a result, 1-naphthol and 2-naphthol are less likely to be formed than naphthalene.