Write the relation for (i) the distance of closest approach and (ii) impact parameter.

Explanation

Distance of closest approach. It is the minimum distance upto which an `alpha`-particle travelling directly towards the centre of the nucleus can move before coming to rest and then retrace its path.
Impact parameter of `alpha`-particle is defined as the perpendicular distance of the velocity vector of `alpha`-particle from the centre of the nucleus, when it is far away from the atoms.