The correct sequence of electron gain enthalpy of the elements listed below isA. ArB. BrC. FD. S

The electron gain enthalpy (or electron affinity) is the amount of energy released when an electron is added to a neutral atom to form a negative ion.

The electron gain enthalpy generally increases across a period (from left to right) on the periodic table and decreases down a group (from top to bottom). This is because as we move across a period, the atomic size decreases and the nuclear charge increases, which makes it easier for the atom to attract an additional electron. On the other hand, as we move down a group, the atomic size increases, which makes it harder for the atom to attract an additional electron.

Given the elements Ar (Argon), Br (Bromine), F (Fluorine), and S (Sulfur), we can use their positions on the periodic table to determine the correct sequence of electron gain enthalpy.

1. F (Fluorine) is in the second period and group 17, so it has the highest electron gain enthalpy.
2. Br (Bromine) is below Fluorine in group 17, so it has the second highest electron gain enthalpy.
3. S (Sulfur) is in the third period and group 16, so it has the third highest electron gain enthalpy.
4. Ar (Argon) is a noble gas in the third period and group 18, so it has the lowest electron gain enthalpy because noble gases have a full valence shell and do not readily gain or lose electrons.

So, the correct sequence of electron gain enthalpy from highest to lowest is F > Br > S > Ar.