The correct answer is A. Natural gas.
Natural gas is a fossil fuel formed when ancient plant and animal remains were buried and subjected to intense heat and pressure over millions of years. It is a mixture of gases, primarily methane, but also ethane, propane, butane, and other hydrocarbons. Natural gas is a clean-burning fuel that produces fewer emissions than other fossil fuels, such as coal and oil. It is also a relatively abundant resource, and its production is expected to continue to increase in the coming years.
Water gas is a mixture of carbon monoxide and hydrogen produced by passing steam over red-hot coke. It is a flammable gas that was once used as a fuel for lighting and heating. However, it has since been replaced by other, more efficient fuels.
Coal gas is a mixture of gases produced by heating coal in the absence of air. It is a flammable gas that was once used as a fuel for lighting and heating. However, it has since been replaced by other, more efficient fuels.
Indane gas is a liquefied petroleum gas (LPG) that is used for cooking and heating. It is a mixture of propane and butane, and it is a clean-burning fuel that produces fewer emissions than other fossil fuels, such as coal and oil.
In conclusion, natural gas has the highest calorific value of the four gases listed.