Question

Arrange F, Cl, Br and I in the order of increasing electronic gain
enthalpy.

Answer 1

increasing  order of electron gain enthalpy is
I<Br<F<Cl.
Cl has highest electron gain enthalpy in periodic table.

Answer 2

The increasing order of electronic enthalpy is given below:

Cl < F < Br < I

In periodic table, down in the group means from "top to bottom", the electron gain enthalpy becomes "less negative". This is because of increasing in size from F to I.

"Electron gain enthalpy" is termed as the energy change when we add "electron to the valence shell" to a gaseous atom which is neutral.

In case of halogens, fluorine shows "less negative" electron gain enthalpy when compared to chlorine because of small size and $2s^2, 2p^5 \ \text {configuration}$.