Which of the following element has the highest ionisation enregy ?

Options

A. nitrogen
B. oxygen
C. carbon
D. boron

Answer

A

Explanation

All these element belong to the `2nd` priod. In general, the ionization potential increases on moving across the period on account of increase of nuclear charge. However, oxygen has unexpectedly lower ionization potential because after the loss of an electron, it ecquires a stable electron, it ecquires a stable electron configuration in the form of excactly half-full `p` subshell:
`O(1s^(2)2s^(2)2p^(4))overset(-e^(-))rarrO (1s^(2)2s^(2)2p^(3))`