What is A in the following reaction?

The correct sequence of correct reagents for the following transformation is :

The equilibrium constant for the reaction

A(s) $$\rightleftharpoons$$ M(s) + $${1 \over 2}$$O₂(g)

is K_p = 4. At equilibrium, the partial pressure of O₂ is _________ atm. (Round off to the nearest integer)

When 400 mL of 0.2 M H₂SO₄ solution is mixed with 600 mL of 0.1 M NaOH solution, the increase in temperature of the final solution is __________ $$\times$$ 10^$$-$$2 K. (Round off to the nearest integer).

[Use : H⁺ (aq) + OH^$$-$$ (aq) $$\to$$ H₂O : $$\Delta$$_$$\gamma$$H = $$-$$57.1 kJ mol^$$-$$1]

Specific heat of H₂O = 4.18 J K^$$-$$1 g^$$-$$1

density of H₂O = 1.0 g cm^$$-$$3

Assume no change in volume of solution on mixing.