Will a gas with a vapor density of 2.6 rise, fall, or have neutral buoyancy in air?

To understand why a gas with a vapor density of 2.6 will fall in air, it's essential to comprehend the concept of vapor density in relation to air's density. Air has an average vapor density of approximately 1.0. When a gas has a vapor density greater than this, it means that the gas is heavier than air.

In this case, a vapor density of 2.6 indicates that the gas is more than double the density of air. Therefore, due to its weight, the gas will not rise or remain suspended; instead, it will tend to fall to the ground as it is unable to stay buoyant amid lighter air molecules. Gases with higher vapor densities than that of air will typically settle downwards, leading to their classification as being heavier than air, which confirms that the correct answer is that the gas will fall.