Answer
$CN^-(aq) + N{H_4}^+(aq) \lt -- \gt HCN(aq) + NH_3(aq)$
Work Step by Step
1. Write the reaction where the reactants exchange theirs cations/anions:
$NaCN(aq) + NH_4Br(aq) \lt -- \gt NaBr(aq) + NH_3(aq) + HCN(aq)$
** When $NH4^+$ reacts with $CN^-$, it produces an acid.
2. Identify the 100% dissociated/ionizated compounds, and separate them in ions:
$Na^+(aq) + CN^-(aq) + N{H_4}^+(aq) + Br^-(aq) \lt -- \gt Na^+(aq) + Br^-(aq) + NH_3(aq) + HCN(aq)$
Salts: Totally dissociated.
3. Eliminate the repeated ions/molecules:
$CN^-(aq) + N{H_4}^+(aq) \lt -- \gt HCN(aq) + NH_3(aq)$
- This is the net ionic equation.
