Which gas is lighter than air and disperses easily?

The correct choice for identifying a gas that is lighter than air and disperses easily is natural gas. Natural gas is primarily composed of methane, which is indeed lighter than air. Because of its lower density, natural gas rises and disperses quickly in the environment, making it less likely to accumulate in low-lying areas where it could pose an explosion hazard.

Propane and butane, on the other hand, are heavier than air. Propane tends to pool in low areas if released and can create dangerous situations due to its potential accumulation. Butane, similarly, is heavier than air and does not disperse as readily as lighter gases.

Ethane is also heavier than air, similar to propane and butane.

In summary, natural gas is the gas that meets the criteria of being lighter than air and dispersing easily, while propane, butane, and ethane do not exhibit these characteristics.