Question

Which of the following processes involves absorption of energy and why?
a) Cl --> Cl-
b)O- --> O2-
c) O+ --> O-
d) S --> S-

Answer 1

b) o to o2- because of interelectronic repulsion it will require energy to add electron to its outermost shell .

Answer 2

Answer: Option (b) is the correct answer.

Explanation:

If we add an electron to an electron deficient atom then it will readily accept it  in order to attain stability and in that case less absorption of energy will take place.

On the other hand, if we add an electron to an electropositive atom then it will also readily accept it because opposite charges attract each other.

Whereas if we add an electron to an anion then there will be repulsion as like charges repel each other. So, great amount of heat needs to be provided in order to add an electron. Hence, absorption of energy will take place in that case.

Thus, we can conclude that out of the given options $O^{-} \rightarrow O^{2-}$ is the process that involves absorption of energy.