Two bodies of different masses are dropped simultaneously from the top of a tower. If air resistance is proportional to the mass of the body,

Air resistance is proportional to mass of the body

$\mathrm{a}=\frac{\mathrm{mg}-{\mathrm{f}}_{\mathrm{air}}}{\mathrm{m}}=\frac{\mathrm{mg}-\mathrm{m\alpha }}{\mathrm{m}}=\mathrm{g}-\mathrm{\alpha }$

This acceleration is independent of mass and hence same time will be required.