What happens when Hinsberg derivative is added to acidic solution?
" compound produces a solid" indicates that a reaction has occured.(hence no 3° amine group(according to this)). Further this is insoluble in base so there is a 2° amine group.

"This solid dissolves in acid" directly implies that there is a 3° amine group.

Hence there is both 2° amine group as well as 3° amine group in the compound.

Hence option b is the correct answer.

References:
1. Solomon and Fryle Hinsberg Test