Explanation:
Divers use tanks to breathe underwater. The air that is filled in these tanks is not pure oxygen as it can be dangerous to breathe pure oxygen underwater. Hence, the air is diluted with another gas to make it safe for the divers to breathe. The gas that is commonly used for this purpose is Helium.

Reasons why Helium is used:
1. Low Density: Helium is a lighter gas than air, which makes it easier for divers to carry their tanks while swimming underwater.

2. Low Solubility: Helium is not easily soluble in the bloodstream, which means that it does not cause any harmful effects on the body even if the diver stays underwater for a longer period.

3. Low Narcotic Effect: Nitrogen, which is present in the air we breathe, can cause a narcotic effect on the body at high pressures. This effect can impair the diver's judgment and motor skills. However, Helium does not have such an effect.

Other gases that can be used:
While Helium is the most commonly used gas for diving, there are other gases such as Argon and Nitrogen that can also be used for this purpose. However, these gases have certain limitations and are not as safe as Helium.

Conclusion:
In conclusion, Helium is used to dilute the air in diving tanks as it is a safe gas that does not cause any harmful effects on the body. It is important for divers to understand the properties of the gas used in their tanks to ensure their safety while underwater.