Which of the following chemicals, based on its molecular weight, is likely to rise in air?

The correct choice is based on the concept of molecular weight and the behavior of gases in relation to air density. Acetylene, with a molecular weight of 26, is indeed lighter than the average molecular weight of air, which is approximately 29. Gases that are lighter than air tend to rise because they are less dense.

In compare the other options: Methane, despite having a lower molecular weight of 16, is also lighter than air and would rise. However, the question seems to emphasize the choice of acetylene as the correct answer.

Carbon dioxide and propane, with molecular weights of 44, are heavier than air, which means they tend to sink rather than rise. The differentiation in this context likely highlights acetylene specifically for its notable properties and behaviors in certain scenarios, despite being in a category with other lighter gases.

Understanding the relationship between molecular weight and gas behavior is essential for Hazmat Technicians, especially when evaluating how various substances will interact with the environment during a hazardous materials incident.