You're asking for the six gases that are less dense than air. However, there are actually many gases less dense than air! Air itself is a mixture of gases, primarily nitrogen (N2) and oxygen (O2).

Here are six examples of gases less dense than air:

1. Hydrogen (H2): The lightest element, hydrogen is significantly less dense than air. It's used in balloons and airships due to its buoyancy.

2. Helium (He): Another very light gas, helium is used in party balloons and for lifting in scientific applications.

3. Methane (CH4): This flammable gas is the main component of natural gas and is less dense than air.

4. Neon (Ne): A noble gas, neon is used in advertising signs due to its colorful glow.

5. Ammonia (NH3): A pungent gas, ammonia is used in fertilizers and other industrial applications.

6. Argon (Ar): A noble gas, argon is used in welding and other industrial processes.

It's important to note that density can vary depending on temperature and pressure. However, the gases listed above are generally less dense than air under standard conditions.