Depression in Freezing point can be calculated as,
ΔTf=i×Kf×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.