Initially electron is in excited state ,

Now,

Incident electron energy .

So, it is capable of exciting it to state. In that case, some part of the KE of incident electron would be converted into of exciting electron.

Thus, collision would be inelastic [as KE is not conserved]. If the excited hydrogen atom de-excited to , then the electron does not lose its kinetic energy, instead gain some kinetic energy. It is the case of superelastic collision.

If -atom were in ground state and incident electron energy were less than which is equal to . Then, collision would always be elastic.

──────────────────────────────────────────────────────────────────────────────────────────