A litre of buffer solution contains 0.1 mole of each of NH$$_3$$ and NH$$_4$$Cl. On the addition of 0.02 mole of HCl by dissolving gaseous HCl, the pH of the solution is found to be _____________ $$\times$$ 10$$^{-3}$$ (Nearest integer)

[Given : $$\mathrm{pK_b(NH_3)=4.745}$$

$$\mathrm{\log2=0.301}$$

$$\mathrm{\log3=0.477}$$

$$\mathrm{T=298~K]}$$

If the pKa of lactic acid is 5, then the pH of 0.005 M calcium lactate solution at 25$$^\circ$$C is ___________ $$\times$$ 10$$^{-1}$$ (Nearest integer)

The dissociation constant of acetic acid is $$x\times10^{-5}$$. When 25 mL of 0.2 $$\mathrm{M~CH_3COONa}$$ solution is mixed with 25 mL of 0.02 $$\mathrm{M~CH_3COOH}$$ solution, the pH of the resultant solution is found to be equal to 5. The value of $$x$$ is ____________

If the solubility product of PbS is 8 $$\times$$ 10^$$-$$28, then the solubility of PbS in pure water at 298 K is x $$\times$$ 10^$$-$$16 mol L^$$-$$1. The value of x is __________. (Nearest Integer)

[Given : $$\sqrt2$$ = 1.41]