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.

All the elements are arranged by melting points on the periodic table. in row they go from metals to gasses. in the row from sodium to argon, sodium is more reactive than the one on its right, magnesium.