What happens to freezing point of benzene when small quantity of napthalene is added to benzene?

Depression in Freezing point can be calculated as,

$∆{\mathrm{T}}_{\mathrm{f}}=\mathrm{i}\times {\mathrm{K}}_{\mathrm{f}}\times \mathrm{m}$

When a non-volatile component is added to the solvent, its freezing point decreases. Here, Napthalene is a non-volatile substance which decreases the freezing point of benzene.

On addition of naphthalene to benzene there is depression in freezing point of benzene.

Hence, the answer is option D.