Consider the following reactions : <br> $(a) \; H^+_{(aq)} + OH^- _{(aq)} = H_2O_{(l)}, \Delta H = -X_1kJ\; mol^{-1}$ <br> $(b)\; H_{2(g)} + \frac{1}{2} O_{2(g)} = H_2O_{(l)}, \Delta H = -X_2 kJ mol^{-1} $ <br> $(c)\; CO_{2(g)} + H_{2(g)} = CO_{(g)} + H_2O_{(l)} -X_3 kJ mol^{-1}$ <br> $(d)\; C_2H_{2(g)} + \frac{5}{2} O_{2(g)} = 2CO_{2(g)} + H_2O_{(l)} +X_4 kJ mol^{-1}$ <br> Enthalpy of formation of $H_2O_{(l)} $ is:

Question

( A ) $- X_4 kJ mol^{-1}$
( B ) $+ X_1 kJ mol^{-1}$
( C ) $+ X_3 kJ mol^{-1}$
( D ) $- X_2 kJ mol^{-1}$