In which of the following pairs the two species are not isostructural ?

The incorrect expression among the following is :

The pH of a 0.1 molar solution of the acid HQ is 3. The value of the ionization constant, K_a of this acid is :

The equilibrium constant (K_C) for the reaction N₂(g) + O₂(g) $$\to$$ 2NO(g) at temperature T is 4 $$\times$$ 10^–4. The value of K_C for the reaction, NO(g) $$\to$$ 1/2N₂(g) + 1/2O₂(g) at the same temperature is :