Which among the following species can act as an acid as well as a base according to the Brønsted-Lowry theory?

Which one is not an acid salt?

Discuss the factors affecting acid strength with examples.

Given:
$(i) \ HCN_{(aq)} + H_2O_{(l)} \rightleftharpoons H_3O^{+}_{(aq)} + CN^{-}_{(aq)}$
$K_a = 6.2 \times 10^{-10}$
$(ii) \ CN^{-}_{(aq)} + H_2O_{(l)} \rightleftharpoons HCN_{(aq)} + OH^{-}_{(aq)}$
$K_b = 1.6 \times 10^{-5}$
These equilibria show the following order of the relative base strength:

Which of the following $0.1 \ M$ solution will contain the largest concentration of hydronium ions?

Which of the following bases is the weakest?