Answer:
NF3< H2S< H2O< He
Explanation:
The average speed of a gas depends on the relative molecular mass of the gas. Lighter gases have a greater average speed and move faster than heavier gases.
Hence, we need to arrange these gases listed in the question in order of decreasing molecular mass in order to obtain the order of increasing Urms assuming equivalent amounts and all gases are at the same temperature and pressure.
Hence; NF3< H2S< H2O< He
