Question

In which of the following , the electron affinity of the second element is more than that of the first element is :

• A. $(F,Cl)$
• B. $(C,N)$
• C. $(N,O)$
• D. $(O,S)$

Answer 1

Answer: (A), (C), (D)

$(O,S)$

Electron affinity is defined as the enthalpy change when one electron is added to a neutral gaseous atom to form a uni negative ion.
In between $F$ and $Cl$, fluorine has the lesser electron affinity due to its small size and repulsion between existing electrons and incoming electrons.
$N$ has lesser electron affinity than $C$ due to its stable electronic configuration.

Along the period, the electron affinity increases from left to right due to increase in nuclear charge. So, $N$ has less electron affinity than $O$ and $B$ has less electron affinity than $C$.
In between $O$ and $S$, oxygen has lesser electron affinity due to its small size and repulsion between existing electrons and incoming electrons.