Question

For electron affinity of halogens which of the following is correct?
A.$Br > F$
B.$F > Cl$
C.$Br > Cl$
D.$F > I$

Answer 1

Hint: Electron affinity: This is defined as the property of elements to attract the electrons of other elements towards it. The higher the electron they will attract the higher will be their electron affinity.

Complete step by step solution:
First of all let us talk about periodic tables.
Periodic table: It is defined as the table in which elements are arranged in a systematic order.
In the periodic table there are two sections: group and period.
Group: They are the vertical lines in the periodic table. There are total $18$ groups in a periodic table. And the names of these groups are as group $1$, group $2$, and so on.
Periods: They are the horizontal lines in the periodic table. There are total $7$ periods in a periodic table. And they are named as period $1$, period $2$, and so on.
The properties (physical and chemical) for the same group elements are almost the same. Because they have the same number of valence electrons in their outer shells.
Group $17$ elements are fluorine, chlorine, bromine, iodine and astatine. They are known as the halogen family. They all have $7$ electrons in their outermost shell. They all need $1$ more electron to complete their octet (eight electrons in the outermost shell). If the element has eight electrons in its outermost shell then they are highly stable and will have less energy. So every element wants to complete its octet.
Electron affinity: This is defined as the property of elements to attract the electrons of other elements towards it. The higher the electron they will attract the higher will be their electron affinity.
Now if we look in a group then on moving down a group from top to bottom electron affinity of an element generally decreases. Because as we move down in a group then the size of the element increases. So the ability to hold electrons decreases hence its electron affinity decreases. So the order of electron affinity for these electrons should be $As < I < Br < Cl < F$. But the actual order of electron affinity is as $As < I < Br < F < Cl$ because the size of fluorine is small so in fluorine atoms there is more repulsion between the electrons. Hence there will be difficulty to hold one more electron in the atom. Hence the electron affinity of chlorine is greater than that of fluorine.

Hence, option (D) is correct.

Note: Noble gases are helium, neon, argon, krypton, xenon and radon. They are known as noble gases because they do not react with other elements under normal conditions. They are stable in its elemental form because they have a complete filled octet.