Final answer:
The relative density of natural gas to air is less than 1, meaning natural gas is lighter than air and will tend to rise.
Step-by-step explanation:
The relative density of natural gas to air is less than 1. This means that natural gas is lighter than air and will tend to rise. Natural gas, composed chiefly of methane, has a density of about 0.67 g/L while air has a density of about 1.29 g/L.