Which gas is produced due to the burning of fuels? 

Carbon dioxide 

The correct answer is option 2. Carbon dioxide.

The gas produced due to the burning of fuels is Carbon dioxide.

When fuels undergo combustion (burning), they react with oxygen in the air to produce carbon dioxide \((CO_2)\) along with water vapor and heat. The general chemical equation for the combustion of a hydrocarbon fuel, such as gasoline or natural gas, is represented as follows:

\[ \text{Fuel} + \text{Oxygen} \rightarrow \text{Carbon Dioxide} + \text{Water Vapor} + \text{Heat} \]

Therefore, carbon dioxide is a common product of the combustion process when fuels are burned.