Ionization energies of $c{l}^{-}$, $cl$ and $c{l}^{+}$ are respectively (in kJ/mol) :

Ionization energies of $c{l}^{-}$, $cl$ and $c{l}^{+}$ are respectively (in kJ/mol) are 2300,349, 1261.

Ionization energy, sometimes referred to as ionization potential, is the quantity of energy needed to remove an electron from an isolated atom or molecule in physics and chemistry.

Therefor, option C is correct.