The OH^$$-$$ concentration in a mixture of 5.0 mL of 0.0504 M NH₄Cl and 2 mL of 0.0210 M NH₃ solution is x $$\times$$ 10^$$-$$6 M. The value of x is ___________. (Nearest integer)

[Given K_w = 1 $$\times$$ 10^$$-$$14 and K_b = 1.8 $$\times$$ 10^$$-$$5]

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)

PCl₅ $$\rightleftharpoons$$ PCl₃ + Cl₂

K_c = 1.844

3.0 moles of PCl₅ is introduced in a 1 L closed reaction vessel at 380 K. The number of moles of PCl₅ at equilibrium is ______________ $$\times$$ 10^$$-$$3. (Round off to the Nearest Integer)

Assuming that Ba(OH)₂ is completely ionised in aqueous solution under the given conditions the concentration of H₃O⁺ ions in 0.005 M aqueous solution of Ba(OH)² at 298 K is ______________ $$\times$$ 10^$$-$$12 mol L^$$-$$1. (Nearest integer)