Calculate the $[\mathrm{OH}]$ if pOH of solution is 4.94

Which from following mixtures in water acts as a basic buffer?

Calculate the pH of a buffer solution containing 0.35 M weak acid and 0.70 M of its salt with strong base if $\mathrm{pK}_{\mathrm{a}}$ is 4.56 .

Calculate the concentration of weak monobasic acid if its degree of dissociation and dissociation constant are $5.0 \times 10^{-4}$ and $5.0 \times 10^{-9}$ respectively.