The bubbles that rise to the surface of the boiling water contain air.
To understand this, we need to know that when water boils, it undergoes a phase change from a liquid to a gas. As the temperature of the water increases, the water molecules gain enough energy to escape from the liquid phase and turn into water vapor, which is a gas.
The bubbles we see are formed when the water vapor tries to escape from the liquid and rises to the surface. These bubbles are primarily composed of air, which is a mixture of various gases, including nitrogen, oxygen, and small amounts of other gases.
Therefore, the correct answer is (i) air.