Question

the force of gravitation between two bodies having irregular shape is taken to be acting at a distance between their.....
a) centre of mass
b) centre of body
c) edge of the body

Answer 1

here is your answer

a) centre of mass

Answer 2

a) centre of mass
because,In a uniform gravitational field the centre of gravity is identical to the centre of mass, a term preferred by physicists. The two do not always coincide, however. For example, the Moon’s centre of mass is very close to its geometric centre (it is not exact because the Moon is not a perfect uniform sphere), but its centre of gravity is slightly displaced toward Earth because of the stronger gravitational force on the Moon’s near side.