Oxygen

Oxygen keeps us alive, and this 11-question quiz takes a closer look at what it actually is and how it behaves.

Expect fill-in-the-blank prompts like Oxygen is the by-product of ___. alongside true or false checks about its color, taste, and the elements it bonds with.

Here is something many learners do not expect: the word oxygen means "acid producer." Scientists once believed oxygen was part of every acid, which turned out to be wrong, but the name stuck anyway.

Recommended level: beginner.