Which of the following is used as an industrial fuel?

Coal gas

The correct answer is option 1. Coal gas.

Out of the options you listed, only one is commonly used as an industrial fuel Coal gas.

Coal gas, also known as manufactured gas or town gas, is a historical fuel produced by heating coal in an oxygen-limited environment. It's a mixture of various gases, including hydrogen, methane, carbon monoxide, and other hydrocarbons. While its use has declined significantly due to the availability of cleaner and more efficient natural gas, it was once a prominent industrial fuel source.

Nitrogen gas: Nitrogen gas itself is not a fuel. It is the main component of air (around 78%) and is relatively inert, meaning it doesn't readily react with other elements to produce heat energy.

Carbon dioxide gas: Similar to nitrogen, carbon dioxide \((CO_2)\) is not a fuel source. It's a greenhouse gas produced by the combustion of fuels.