Neutralization is the reaction between acid and base.It is highly exothermic.Enthalpy of neutralization is least for the reaction

For a strong acid and strong base reaction, the net reaction isH++OH-→H2O ; ∆H=-57.3 kJ/moleBoth HCN and NH4OH are weak electrolytes. They absorb energy for their ionization. Net heat liberated during the reaction is minimum.