Why is force not on a scalar quantity? ?

Because force always has a direction, it always works towards or against something.

you might know that force,
is rate of change of momentum i.e

force = m (v-u)/t
= (mv - mu )/ t

as we know momentum is a vector quantity so, the rate of change of momentum i.e Force would also be a vector quantity.

momentum = mass × velocity

velocity has a direction so,
momentum has also got a direction.
so, momentum is also a vector quantity.

Then the answer would be d then