Multiple choice general knowledge

Which one of the following substances is made up of only one type of atoms?

  1. water

  2. milk

  3. hydrogen

  4. air
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Hydrogen is an element consisting of only hydrogen atoms (H₂ molecules). Water (H₂O) contains hydrogen and oxygen atoms. Milk is a complex mixture of water, fats, proteins, and sugars. Air is a mixture of nitrogen, oxygen, carbon dioxide, and other gases.

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