Which of the following is an example of a compound? Gold (Au)Oxygen gas (O2)Water (H2O)Helium gas (He)

The example of a compound from the given options is Water (H2O).

Here's why:

A compound is a substance formed when two or more chemical elements are chemically bonded together.

1. Gold (Au) is an element, not a compound because it consists of only one type of atom.
2. Oxygen gas (O2) is a molecule, not a compound because it consists of only one type of atom.
3. Water (H2O) is a compound because it is made up of two different elements - Hydrogen and Oxygen.
4. Helium gas (He) is an element, not a compound because it consists of only one type of atom.