A) \(1 s\, 2 s\)

B) \(1 s ^2 \,2 s ^2 \,2 p\)

C) \(1 s^2\, 2 s^2 \,2 p^5\)

D) \(1 s ^2 \,2 s ^2 2 p^6\)

From the options above we notice that the greatest energy will be involved for option \(C\) as it has attained the noble gas configuration after the loss of \(2\) electrons and removal of a \(3\) electron will require a lot of energy.