Saturated solution of $KN{O}_3$ is used to construct ‘salt – bridge’ because

$KN{O}_3$ is highly soluble in water

Velocity of $K^{+}$  is greater than that of  ${\mathrm{NO}}_3^{-}$

Velocity of ${\mathrm{NO}}_3^{-}$ is greater than that of $K^{+}$

Velocities of both $K^{+}$ and ${\mathrm{NO}}_3^{-}$ are nearly the same