The first ionization energy of oxygen is less than that of nitrogen. Which of the following is the correct reason for this observation?

Options

A. Lesser effective nuclear charge of oxygen than nitrogen
B. Lesser atomic size of oxygen than nitrogen
C. Greater inter–electron repulsion between two electrons in the same p orbital counter balances the increase in effective nuclear charge on moving from nitrogen to oxygen
D. Greater effective nuclear charge of oxygen than nitrogen

Answer

C

Explanation

First ionization potential of oxygen is less than nitrogen because N have a half filled p - orbital which further stabilize to the atom.
`""_7N = 1s^2 2s^2 2p^3` (Half filled orbital)
`""_8O = 1 s^2 2s^2 2p^4` (More than half filled orbital)
`p^3 gt p^4` (stability order)