A Level Physics Practice Exam

The process that allows atoms to absorb energy from colliding electrons without being ionized is excitation. When an atom is excited, energy is transferred to one of its electrons, promoting it to a higher energy level within the atom. This process occurs when the energy from the colliding electrons is sufficient to excite the electrons but not enough to completely remove them from the atom, which is what would happen in ionization.

Ionic bonding involves the transfer of electrons between atoms to form charged ions, and photon absorption refers to the process where an atom absorbs a photon of light, which may or may not lead to excitation depending on the photon's energy. Electron capture is a distinct process in which a proton-rich nucleus captures one of its inner electrons, leading to a transformation of a proton into a neutron. Thus, excitation is the correct answer as it describes the specific interaction between colliding electrons and atom's electrons that results in a higher energy state without ionization.