In the laboratory setup shown below, an upside-down beaker has been partially filled with the gaseous form of hydrogen \(\left(\mathrm{H}_{2}\right)\) , which is the lightest element.

What is occurring in the illustration?

Explanation

Hydrogen diffuses (moves to mix with other gases) more quickly than any other element. Thus, in the illustration, it is moving through the porous cup wall to mix with the air in the cup. This forces the air in the tube down into the water, from which that air escapes in the form of bubbles.

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