DH^o of water is -285.8 kJ mol^-1 . If enthalpy of neutralization of monoacid strong base is

-57.3kJ mol^-1, DH^o of OH^- ion will be

D${\mathrm{H}}_{\mathrm{f}}^{°}$ water = -285.8kJ.mol^-1

D${\mathrm{H}}_{\mathrm{f}}^{°}$ of strong base and mono acid neutralization = -57.3kJ mol^-1

D${\mathrm{H}}_{\mathrm{f}}^{°}$ of OH^- ion = ?

x = y - z

x = -285.8 - (-57.3)

$\mathcal{x}=-228.5kJmo{l}^{-1}$