Which reaction is not feasible?

2 mole of ideal gas at 27^oC temperature is expanded reversibly from 2 lit. to 20 lit. Find entropy change. (R = 2 cal/mol K)

Solubility of MX₂ type electrolytes is 0.5 $$ \times $$ 10^$$-$$4 mole/lit., then find out K_sp of electrolytes.

Reaction BaO_2(g) $$\rightleftharpoons$$ BaO_(s) + O_2(g); $$\Delta $$H = +ve. In equilibrium condition, pressure of O₂ depends on