The process requiring the absorption of energy is (are):

Options

A. Cl-`Cl^-`
B. `O^(-)toO^(2-)`
C. `Fe^(2+)toFe^(3+)`
D. `ArtoAr^(-)`

Answer

B,D

Explanation

(B)Addition of second electron to `O^-` is opposed by electrostatic repulsion due to same charge. Hence energy is given for the addition of second electron.
(D)Ar has stable electronic configuration `(ns^2 np^6)` .Hence energy has to be given to add an extra electron to from `Al^-`.