Question

The correct order of electron affinity is,
A. $O$ > $F$ >$Cl$
B. $F$> $O$ > $Cl$
C. $F$ > $Cl$ >$O$
D. $Cl$> $F$> $O$

Answer 1

On moving from left to right across a period, the electron affinity becomes more negative. On moving from top to bottom in a group, the electron affinity becomes less negative.

Complete step by step solution:
First we consider fluorine and chlorine. Chlorine has more negative electron affinity than fluorine. Because adding an electron to fluorine 2p orbital causes greater repulsion than adding an electron to chlorine 3p orbital which is larger in size. Fluorine is very small in size, and its electrons are ‘compressed’ in this space. Because of this, interelectronic repulsion happens, causing the incoming electron to be repelled. So chlorine ends up having more electron affinity than $F$. In fact, Chlorine has the most electron affinity of all elements. Which is present in only one option that is $Cl$> $F$>$O$.

**So the correct option is D. $Cl$> $F$>$O$.

Note: **
The electron affinity (in kJ/mol) Chlorine ($Cl$), Fluorine ($F$) and Oxygen ($O$) is -349, -328, -141 respectively. Chlorine has the highest electron affinity among all the electrons.