The term electron capture best fits which of the following descriptions? A. Electron capture is a phenomenon exhibited by an unstable nucleon that spontaneously converts into a more stable nuclei.
B. Electron capture is the combination of a core electron with a proton to yield a neutron within the nucleus.
C. Electron capture is the addition of an electron to a neutral atom to form an anion.
D. None of the above.

Option B:

Electron capture is the combination of a core electron with a proton to yield a neutron within the nucleus.

Explanation:

The electron capture is a nuclear process whereby a neutral atom absorbs an electron from its closest shell (which is usually the K shell of the atom).

This capture phenomenon, causes one of the protons within the nucleus of the atom to convert into a neutron because of the merging of the positive and negative charges. Once they merge, a light particle called the electron neutrino is emitted from the nucleus of the atom.

This phenomenon occurs mostly in atoms that have a proton-rich nucleus. This provides the positive charge that pulls the electron from its shell into the nucleus of the atom.