The heats of combustion of ethane, ethene and acetylene are –341.1, –330 and –310.9K.Calmol^–1 respectively. The best fuel among them is

Calorific value (CV): amount of energy released per gram is called calorific value

Quality of fuel increases with increase in calorific value 

$\text{CV=}\frac{ \mathrm{Heat} \mathrm{of} \mathrm{combustion} }{\mathrm{MW}}$

Ethane, $CV=\frac{\mathrm{H} \mathrm{eat} \mathrm{of} \mathrm{cambustton} }{\mathrm{MW}}=-\frac{341.1}{30}=11.37\mathrm{KJ}/\mathrm{g}$

Ethene, $CV=\frac{H\text{ eat of cambustton }}{MW}=-\frac{330}{28}=11.78\mathrm{KJ}/\mathrm{g}$

Acetylene, $CV=\frac{\text{ Heat of cambustion }}{MW}=-\frac{310.9}{26}=11.95\mathrm{KJ}/\mathrm{g}$

Acetylene have best CV value and hence is the best fuel 

Hence the correct option is (C).