Answer:
CN⁻(aq) + H⁺(aq) ⇒ HCN(aq)
Explanation:
Let's consider the following molecular equation.
NaCN(aq) + HI(aq) ⇒ NaI(aq) + HCN(aq)
HI is a strong electrolyte so it exists mostly in the ionic form. HCN is a weak electrolyte so it exists mostly in the molecular form.
The full ionic equation includes all the ions and the molecular species.
Na⁺(aq) + CN⁻(aq) + H⁺(aq) + I⁻(aq) ⇒ Na⁺(aq) + I⁻(aq) + HCN(aq)
The net ionic equation includes only the ions that participate in the reaction and the molecular species.
CN⁻(aq) + H⁺(aq) ⇒ HCN(aq)