d
\(\mathop {HCl}\limits_{Strong\,acid}  \to \mathop {{H^ + } + C{l^ - }}\limits_{Complete\,ionisation....(i)} \)

\(\mathop {N{H_4}OH}\limits_{Weak\,base}  \leftrightarrow \mathop {NH_4^ +  + O{H^ - }}\limits_{\Delta H = x\,kJ\,mo{l^{ - 1}}....(ii)} \)

\({H^ + } + O{H^ - } \to {H_2}O\)

             \(\Delta H =  - 55.90\,kJ\,mo{l^{ - 1}}....(iii)\)

             (from neutralisation of strong acid and strong base)

From equation \((i),(ii)\) and \((iii)\)

\(N{H_4}OH + HCl \to NH_4^ +  + C{l^ - } + {H_2}O\)

         \(\Delta H =  - 51.46\,kJ\,mo{l^{ - 1}}\)

\(\therefore x + ( - 55.90) =  - 51.46\)

\(x =  - 51.46 + 55.90\)

\( =  4.44\,kJ\,mo{l^{ - 1}}\)

\(\therefore \) Enthalpy of ionisation of 

\(N{H_4}OH = 4.44\,kJ\,mo{l^{ - 1}}\)