At 320 K, a gas A2 is 20% dissociated to A.

Given that, A2 <=> 2A
Let initial moles of A2 be 1 mole.
At equilibrium:
Moles of A2 = 1 - 0.2 = 0.8 moles
Moles of A = 2(0.2) = 0.4 moles
Total moles at equilibrium = 0.8 + 0.4 = 1.2 moles
Kp = (Partial pressure of A)^2 / (Partial pressure of A2)
Kp = (0.4/1.2)^2 / (0.8/1.2)
Kp = (1/3)^2 / (2/3)
Kp = 1/6
The question is incomplete and does not provide the necessary information to calculate a numerical value. The solution provides the equilibrium expression for Kp. More data, such as total pressure or equilibrium partial pressures, is needed to solve for a numerical answer from the given options.