Let two H atoms initially at in the ground state. Now two atoms collide inelastically. The total energy associated with the two H atoms= 2 x (13.6 eV) = 27.2eV The maximum amount by which their combined kinetic energy is reduced when any one of them goes into first excited state (n = 2) after the inelastic collision. The total energy associated with the two H-atoms after the collision = (
13.6
22
) + (13.6) = 17.0 eV Hence, maximum loss of their combined kinetic energy = 27.2 - 17.0 = 10.2 eV