With which of the following electronic configuration of an atom has the lowest ionization enthalpy :

Question

( A ) $1s^2 2s^2 2p^53s^1$
( B ) $1s^2 2s^2 2p^5$
( C ) $1s^2 2s^2 2p^6$
( D ) $1s^2 2s^2 2p^3$