When a gas collection tube is inverted, which property is typical for the gas?

• A. More dense than air
• B. Less dense than air
• C. Heavier than water
• D. Highly reactive

Answer: (B)

When a gas is collected by inverting a tube over the reaction, density relative to air governs how the gas behaves inside the tube. If the gas is lighter than air, it will rise and fill the upper part of the inverted tube, displacing water as it goes, so you can collect it in the space inside the tube. This makes a gas lighter than air the typical outcome in this setup.

If the gas were heavier than air, it would tend to stay closer to the mouth of the tube and wouldn’t fill the tube as readily, making collection harder. Saying the gas is heavier than water isn’t the controlling factor here, since the collection occurs in air, not in a liquid. Being highly reactive isn’t indicated by the collection method itself.

So, the most fitting property is that the gas is less dense than air.