Which of the following interaction is the weakest           

Gravitational force is the weakest force whereas the nuclear force is the strongest force that exists between the nucleons present in the nucleus.

Gravitational force is given by:

${\text{F}}_{ }=\text{G}.\frac{{\text{m}}_{\text{1}}{\text{m}}_{\text{2}}}{{\text{r}}_{ }^2}$
Where m₁ and m₂ are the masses of the two bodies, r is the distance between them and G is the universal gravitation constant.
$G= 6.67 X {10}^{-11} N{m}^2/k{g}^2$

As the value of G is very small, the gravitational force between two objects is very small until and unless at least one of the masses is very large.

Hence option A is the correct answer.