Consider aiming a beam of free electrons towards free protons.

Consider aiming a beam of free electrons towards free protons. When-they scatter an electron and a proton cannot combine to produce a H-atom.  (a) Because of energy conservation (b) Without simultaneously releasing energy in the form of radiation (c) Because of momentum conservation (d) Because of angular momentum conservation

(a, b) A moving electron and proton cannot combine to produce a H-atom because of energy conservation and without simultaneously releasing energy in the form of radiation.