Given are the following data at 298 K.ΔcH°C2H4,g=−1410.9 kJ mol−1;  ΔcH°C2H6,g=−1559.8 kJ mol−1;   ΔcH°H2 , g=−285.8 kJ mol−1The value of ΔrH° of the reaction C2H4g+H2g→  C2H6g will be

i     C2H4g+3O2g→  2CO2g+2H2O1;             ΔcH°=−1410.9 kJ mol−1ii    C2H6g+72O2g→  2CO2g+3H2O1;            ΔcH°=−1559.8 kJ mol−1iii    H2g+12O2g→  H2O1;                                  ΔcH°=−285.8 kJ mol−1The required chemical equation for which ΔrH° is required is C2H4g+H2g→  C2H6gThis equation is obtained by the manipulations Eq. (i) + Eq. (q. (ii)Hence, ΔrH°=−1410.9−285.8−−1559.8kJ mol−1=−136.9 kJ mol−1