Terminal velocity of a given spherical body in a medium of iscosity $\eta$ is given by

$v= \large\frac{2}{9} $$g (\rho - \sigma)$$ \large\frac{r^2}{\eta}$

Where $ \rho$ density of body

$\sigma$ density of liquid

$r$ radius of spherical body

$v\; \alpha\; r^2$

also mass $\alpha \;r^3$

Momentum = mass $\times$ velocity

Momentum $\alpha\; r^5$

Momentum of drop whose radius is twice is $2^5 P$

$\qquad=32\;P$

Hence d is the correct answer.