Electron gain enthalpy is the energy change when an atom in the gaseous state gains an electron to form a negative ion. A more negative value indicates a greater tendency to gain an electron (higher electronegativity).

For halogens, the general trend down the group is that electron gain enthalpy becomes less negative (decreases in magnitude) due to increasing atomic size and electron-electron repulsions. However, fluorine is an exception.

Fluorine has a less negative electron gain enthalpy than chlorine because:

• Its small size leads to high electron density and significant repulsion when adding an extra electron.
• Chlorine has a larger atomic size, allowing it to accommodate the extra electron more comfortably, resulting in a more negative electron gain enthalpy.

The correct order of electron gain enthalpy (most negative to least negative) is:

Chlorine > Fluorine > Bromine > Iodine

So the values are: Chlorine (-349 kJ/mol), Fluorine (-333 kJ/mol), Bromine (-325 kJ/mol), Iodine (-296 kJ/mol).

Therefore, the correct option is: $-349,-333,-325,-296$

Related Topics

Periodic Trends: Electron gain enthalpy generally becomes less negative down a group and more negative across a period from left to right, with exceptions like fluorine.

Atomic Properties: Atomic size, effective nuclear charge, and electron-electron repulsion influence electron gain enthalpy.

Formulae

Electron gain enthalpy is denoted by $\Delta H_{eg}$. For a generic atom X: $X\left(g\right)+e^{-}\to X^{-}\left(g\right)+\Delta H_{eg}$