$H_2$$_{(g)} +$ $1/2O_2$ $_{(g)}$ $\rightarrow$ $H_2$$O$$_{(l)}$; $\Delta H= -$ $285.77\, KJ\, mol$$^{-1}$; $H_2$$_{(g)} +$ $1/2O_2$$_{(g)}$ $\rightarrow$ $H_2O$ $_{(g)}$; $\Delta H$ $ = - 241.84\, KJ \,mol$$^{-1}$
$(i)$ $N_2H_4$$_{(l)}$ $+$ $2H_2O_2$$_{(l)}$ $\rightarrow$ $N_2$$_{(g)}$ $+$ $4H_2O$$_{(l)}$; $\Delta r{H_1}^ \circ = - 818 \,kJ/mol$
$(ii)$ $N_2H_4$$_{(l)}$ $+$ $O_2$$_{(g)}$ $\rightarrow$ $N_2$$_{(g)}$ $+$ $2H_2O$$_{(l)}$; $\Delta r{H_2}^ \circ = - 622 \,kJ/mol$
$(iii)$ ${H_2}_{(g)}\,\, $+$ \,\,\frac{1}{2}\,{O_2}_{(g)}\,\, \to \,\,{H_2}O_{(l)}\,\,\,;\,\,{\Delta }r{H_3}^ \circ \, = \,\, - 285\,\,kJ/mol$