Which of the following hydrogen bonds is the strongest?

In conversion of lime-stone to lime,
CaCO₃(s) $$\to$$ CaO(s) + CO₂ (g) the vales of ∆H° and ∆S° are +179.1 kJ mol−1 and 160.2 J/K respectively at 298 K and 1 bar. Assuming that ∆H° do not change with temperature, temperature above which conversion of limestone to lime will be spontaneous is :

Identify the correct statement regarding a spontaneous process :

The first and second dissociation constants of an acid H₂A are 1.0 $$\times$$ 10⁻⁵ and 5.0 $$\times$$ 10⁻¹⁰ respectively. The overall dissociation constant of the acid will be :