The reaction 2X $$ \to $$ B is a zeroth order reaction. If the initial concentration of X is 0.2 M, the half-life is 6 h. When the initial concentration of X is 0.5 M, the time required to reach its final concentration of 0.2 M will be:

The reaction, MgO(s) + C(s) $$ \to $$ Mg(s) + CO(g), for which $$\Delta $$_rH^o + 491.1 kJ mol^–1 and $$\Delta $$_rS^o = 198.0 JK^–1 mol^–1, is not feasible at 298 K. Temperature above which reaciton will be feasible is :

K₂Hgl₄ is 40% ionised in aqueous solution. The value of its van't Hoff factor (i) is:

For the equilibrium,
2H₂O $$\rightleftharpoons$$ H₃O⁺ + OH^$$-$$, the value of $$\Delta $$G^o at 298 K is approximately :