Question

Electron gain enthalpy of 17th group elements are -349, -328, -325, -296, -270 KJ/mole (not in order). The element which has electron gain enthalpy -296KJ/mol is:
A. F
B. Cl
C. Br
D. I

Answer 1

Hint: The given elements are halogens. The general electronic configuration of halogen is $n{s^2}n{p^5}$. To attain a stable configuration it required only one electron. The electron gain enthalpy is related with the atomic size of the atom.

Complete answer:The electron gain enthalpy is defined as the quantity of energy released when an electron is added to the neutral atom. The electron gain enthalpy can be negative or positive depending on the energy released and absorbed during the addition of electrons.
The general electronic configuration of halogens is $n{s^2}n{p^5}$, it means halogens require one electron to complete its octet and form a stable atom. So, the halogen can gain electrons easily and become more negative.
The atoms present in the halogen group have higher electron gain enthalpy as compared to other atoms present in the periodic table.
The electron gain enthalpy decreases as we move down in the group as the atomic size increases.
The electron gains enthalpy value of halogens in order is shown below.
(F)-328,(Cl)-349, (Br)-325, (I)-296
Thus, the element which has electron gain enthalpy -296KJ/mol is iodine.
Therefore, the correct option is D.

Note: We can see that the electron gain enthalpy of fluorine is less than chlorine. This is due to the small size of fluorine where electron-electron repulsion is observed, thus the electron gain enthalpy of fluorine is less than chlorine. Thus the order of electron gain enthalpy in halogen is shown below.
$F < Cl > Br > I$