Question

Which element is proposed to have the highest third ionization energy.

		calcium
		germanium
		gallium
		potassium

Answer 1

Ionisation energy is the energy required to remove a electron from a atom in an isolated gaseous state

Third ionization energy means the energy required to remove 3^rd valence electron

Now, Electroic configuration of

Ca = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² and Ca²⁺ = 1s² 2s² 2p⁶ 3s² 3p⁶

Ge = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p² and Ge²⁺ =  1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s²

Ga = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p¹ and Ga²⁺ = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹

K = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹ and K²⁺ = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹

Since Ca²⁺ has electronic configuration equals to the noble gas configuration thus, Calcium have third highest ionisation energy.