Consider the following reactions: (i) H+ (aq) + OH- (aq) = H2O (l) , H = -X 1 kJ mol -1 (ii) H2 (g) + 1 2 O2 (g) = H2O(l) , H = -X 2 kJ mol -1 (iii) CO2 (g) + H2 (g) = CO (g) + H2O , H = -X 3 kJ mol -1 (iv) C2H2 (g) + 5 2 O2 (g) = 2CO2 (g) + H2O(l) , H = -X 4 kJ mol -1 Enthalpy of formation of H2O (l) is

1. A. +X 3 kJ mol -1
2. B. -X 4 kJ mol -1
3. C. +X 1 kJ mol -1
4. D. -X 2 kJ mol -1

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