Which choice can be classified as a pure substance?
A pure substance can be classified as a substance that consists of only one type of atom or molecule.
Choices that can be classified as pure substances include:
1. Oxygen gas (O2): An example of a pure substance as it consists of a molecule comprising only oxygen atoms.
2. Sodium chloride (NaCl): Another example of a pure substance as it consists of a compound made up of only sodium and chloride ions.
3. Gold (Au): A pure substance as it consists of only gold atoms.
4. Water (H2O): A pure substance as it consists of a molecule made up of hydrogen and oxygen atoms in a fixed ratio.
These choices represent examples where the substance has a definite chemical composition and is considered pure because its properties are consistent and uniform throughout.