Which of the following is least likely to behave as Lewis base?

A buffer solution is prepared in which the concentration of NH₃ is 0.30 M and the concentration of NH⁺₄ is 0.20 M. If the equilibrium constant, K_b for NH₃ equals 1.8 $$ \times $$ 10^$$-$$5, what is the pH of this solution? (log 2.7 = 0.43)

If pH of a saturated solution of Ba(OH)₂ is 12, the value of its K_sp is

What is [H⁺] in mol/L of a solution that is 0.20 M in CH₃COONa and 0.10 M in CH₃COOH? K_a for CH₃COOH = 1.8 $$ \times $$ 10^$$-$$5