The energy needed to remove an electron from an atom is called energy.
ejection
ionization
valence
electronegative

 ionization

Explanation:

Ejection of electrons occur when incident light of frequency greater than threshold frequency falls on a metal, the electrons are ejected from metal.

Ionization is the amount of energy requires to remove the most loosely bound electron from an isolated gaseous atom

Valence is the outermost shell which contains the most loosely bound electron.

Electronegativity is the tendency of an atom to attract the shared pair of electrons towards itself.

1. a)c-14 has two more protons

2. d)they have different numbers of protons, neutrons, and valence electrons; they are all gases at room temperature.

3. c) iron and nickel.