For the reaction, X₂O₄(i) → 2XO₂(g), ΔU = 2.1 kcal, ΔS = 20 cal/K at 300 K. Hence, ΔG is:

The correct option is B -2.7 k cal
The relationship between the enthalpy change and the change in internal energy is as shown below.
ΔH = ΔU + ΔnRT
where ΔH is the enthalpy change, ΔU is the change in internal energy, Δn is the change in the number of moles of gas, R is the gas constant, and T is the temperature.
In this reaction, Δn = 2 - 0 = 2 moles.
R = 1.987 cal/mol.K
T = 300 K
ΔH = 2.1 kcal + 2 × 1.987 cal/mol.K × 300 K
ΔH = 2100 cal + 1192.2 cal
ΔH = 3292.2 cal = 3.292 kcal
The Gibbs free energy change (ΔG) is given by:
ΔG = ΔH - TΔS
ΔG = 3292.2 cal - 300 K × 20 cal/K
ΔG = 3292.2 cal - 6000 cal
ΔG = -2707.8 cal
ΔG = -2.7078 kcal ≈ -2.7 kcal