Can hydrogen be collected by air displacement? Why is hydrogen collected in an upside-down test tube?

Can hydrogen be collected by air displacement? Why is hydrogen collected in an upside-down test tube? What happens if the tube is held upside down?

Hydrogen can be collected by air displacement. Because hydrogen is much lighter than air, then it is collected in a test tube, turned upside down. If the tube is kept upside down, the hydrogen will fly upward from it.

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