Write the dissociation reaction and the corresponding ka equilibrium expression for hcn in water

Chemical reaction: HCN(aq) + H₂O(l) ⇄ CN⁻(aq) + H₃O⁺(aq).
Ka = [CN⁻] · [H₃O⁺] / [HCN].
[HCN] is equilibrium concentration of hydrocyanic acid.
hydrocyanic acid is weakly acidic and partially ionizes in water solution and give the cyanide anion (CN⁻).
The salts of the cyanide anion are called cyanides.

Determine the  wavelength of light emitted when an electron  in an li2+ ion  makes a transition from an orbital with n  =  6 to an orbital with n  = 5.