Which one has least ionisation potential?

Options

A. N
B. O
C. F
D. Ne

Answer

B

Explanation

Oxygen has least ionisation potential. In a periodic table, ionisation potential generally increases from loft to right in a period but the first ionisation potential of nitrogen is greater than oxygen because in nitrogen atom, the outermost electron is present in half filled 2p-subshell which is a stable electronic arrangement So, a greater amount of energy is required to pull out one electron from neutral gaseous nitrogen atom.