Consider the following reactions :
(a) `H_((aq))^(+)+OH_((aq))^(-)=H_(2)O_((l)), Delta H= - X_(1)"kJ mol"^(-1)`
(b) `H_(2(g))+(1)/(2)O_(2(g))=H_(2)O_((l)), Delta H= - X_(2)"kJ mol"^(-1)`
(c ) `CO_(2(g))+H_(2(g))=CO_((g))+H_(2)O_((l))- X_(3)"kJ mol"^(-1)`
(d) `C_(2)H_(2(g))+(5)/(2)O_(2(g))=2CO_(2(g))+H_(2)O_((l))+X_(4)"kJ mol"^(-1)`
Enthalpy of formation of `H_(2)O_((l))` is :

Options

A. `+X_(1)kJ mol^(-1) `
B. `-X_(2)kJ mol^(-1)`
C. `+X_(3)kJ mol^(-1)`
D. `-X_(4) kJ mol^(-1)`

Answer

B