An electron collides with a free molecules initially in its ground state. The collision leaves the molecules in
an excited state that is metastable and does not decay to the ground state by radiation. Let K be the sum of
the initial kinetic energies of the electron and the molecule, and P
r
the sum of their initial momenta. Let K'
and P' represent the same physical quantities after the collision. Then -
(A) K = K', P = P' (B) K' < K, P = P' (C) K = K', P ≠ P' (D) K' < K, P ≠ P'