The correct option is C 16 times
Let M1 and M2 be the masses of two objects and R be the distance between them.
The gravitational force, F = GM1M2R2, where G is the universal gravitational constant.
Since M1,M2 and G are constants,
F∝1R2
So, when distance between them is reduced to R4, the force of attraction between them increases to 16times of the initial value.