A moving hydrogen atom makes a head-on in elastic collision with a stationary hydrogen atom. Before collision both atoms are in ground state and after collision they move together. What is minimum velocity of moving hydrogen atom ignore of atoms is to be given the minimum excitation energy after the collision ?

Question

$(a)\;7.2 \times 10^{5} ms^{-1}\qquad(b)\;6.3 \times 10^{4} ms^{-1}\qquad(c)\;8.6 \times 10^{6} ms^{-1}\qquad(d)\;4.2 \times 10^{3} ms^{-1}$