Which of the following fuels has the lowest calorific value?

The correct option is B

${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$

Explanation for correct option:

B. ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$

Calorific value:

• “The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value.”
• The calorific value of a fuel is expressed in a unit called kilojoule per kg $(\mathrm{kJ}{\mathrm{kg}}^{-1})$.
• Among organic fuels, oxygen-containing organic compounds such as alcohols/ethers/aldehydes/ketones have the lowest calorific values.
• Thus, among the given compounds, Ethanol will have the lowest calorific value as it has the lowest percentage composition of hydrogen compared to the others

Explanation for incorrect options:

A. ${\mathrm{C}}_2{\mathrm{H}}_6$

• The calorific value of Ethane is $11350\mathrm{kJ}{\mathrm{kg}}^{-1}$, which is higher than that of Ethanol.

C. ${\mathrm{H}}_2$

• Hydrogen has the highest calorific value which is $150000\mathrm{kJ}{\mathrm{kg}}^{-1}$.

D. ${\mathrm{C}}_2{\mathrm{H}}_4$

• The calorific value of Ethene is higher than ethanol.

Hence, the correct option is B i.e. ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$ has the lowest calorific value.