Which gas is produced when coal burns in air? 

Carbon dioxide 

The correct answer is option 1. Carbon dioxide.

When coal undergoes combustion in the presence of air (which contains oxygen), a chemical reaction occurs. The primary combustion reaction involving carbon in coal can be represented as follows:

\[ C_{(s)} + O_{2(g)} \rightarrow CO_{2(g)} \]

In this reaction:

\( C_{(s)} \) represents solid carbon in coal.

\( O_{2(g)} \) represents oxygen from the air.

The reaction produces carbon dioxide (\( CO_{2(g)} \)) as a result. This is the most common byproduct of the combustion of carbonaceous materials, such as coal. Carbon dioxide is a colorless, odorless gas and a major component of greenhouse gases. It is released into the atmosphere when fossil fuels like coal are burned, contributing to concerns about climate change and global warming due to its role in trapping heat in the Earth's atmosphere.