Statement – I: ${\text{HSO}}_4^{-}$ acts as an acid, according to Bronsted - Lowry theory. 

Statement – II: ${\text{CN}}^{-}$ acts as a base, according to Bronsted - Lowry theory. 

Statement – III: ${\text{H}}_2\text{O}$ acts as a base as well as an acid, according to Bronsted Lowry theory.

According to Bronsted – Lowry theory, acid is proton donor and base is proton acceptor. Hence, ${\text{HSO}}_4^{-}$ can donate a proton whereas${\text{CN}}^{-}$  can accepts proton. Water ${\text{H}}_2\text{O}$ can act as both proton donor as well as proton acceptor. Hence, ${\text{H}}_2\text{O}$ behaves Bronsted – Lowry acid as well base.