Question

if a moving body collides head on elastically with another identical body at rest

Answer 1

if a moving body collides with another identical body at rest of same mass their velocity get exchanged...therefore after  collision velocity  of moving body will be zero and the body which was at rest will start moving with velocity of previously moving body

Answer 2

The body which was moving with a velocity will come to rest after collison and the body which was at rest will acquire the velocity of the first one...