Final answer:
The process described involves collecting hydrogen gas by displacing oxygen gas through the water displacement method, relying on hydrogen being less dense and poorly soluble in water.
Step-by-step explanation:
When a student collects a sample of hydrogen gas by displacement, it is most correctly described as the displacement of oxygen gas. This chemical laboratory technique, called water displacement, involves filling a container with water, inverting it in a pan of water, and directing the gas produced in a reaction through rubber tubing under the water-filled container.
As the hydrogen gas is generated, it exits the tubing, displacing the water in the container because hydrogen is less dense than water and does not dissolve well in water. It's important to consider that oxygen is the only gas from the given options that is significantly present in air and can be displaced by hydrogen during this experiment.
This method also relates to the application of Dalton's Law in collecting gases over water, as the pressure inside the collection container is equalized with atmospheric pressure.