If the values of $ \Delta H_f^{\circ}\: for\: CH_4(g), C_2H_6(g), CO_2(g)\: and \: H_2O(l)$ are respectively $-74.85, -84.68, -393.5 \: and\: -286\: kJ/mol,$ predict which is more efficient fuel?

Question

$\begin {array} {1 1} (A)\;ethane & \quad (B)\;methane \\ (C)\;Both \: are\: equally\: efficient & \quad (D)\;Can’t\: be\: determined \end {array}$