The first electron gain enthalpies of $$F$$, $$Cl$$, $$Br$$ and $$I$$ are given below in a random order:

$$-295,\quad -328,\quad -349,\quad -325;kJ,mol^{-1}$$

Identify and enter the numerical value of the magnitude of electron gain enthalpy of $$Br$$ in $$kJ,mol^{-1}$$.

1. Establish the Halogen Trend

a) The correct decreasing order of negative electron gain enthalpy for halogens is

$$\mathrm{Cl>F>Br>I}$$

b) Fluorine has a slightly lower negative value than chlorine due to significant inter-electronic repulsions in its compact

$$2p$$ subshell.

2. Match Values to Elements

a) $$\mathrm{Cl=-349\ kJ\,mol^{-1}}$$

b) $$\mathrm{F=-328\ kJ\,mol^{-1}}$$

c) $$\mathrm{Br=-325\ kJ\,mol^{-1}}$$

d) $$\mathrm{I=-295\ kJ\,mol^{-1}}$$

3. Extract the Magnitude

a) The electron gain enthalpy value for bromine is

$$-325\ \mathrm{kJ\,mol^{-1}}$$

b) Taking the absolute magnitude gives a final positive value of

$$ Correct  answer: -{325\ \mathrm{kJ\,mol^{-1}}}$$