What are compounds?

Compounds are defined as substances that consist of two or more different elements that are chemically bonded together. This means that the elements combine in fixed proportions through chemical reactions to form new substances with unique properties that differ from those of the individual elements.

For example, water (H₂O) is a compound made from hydrogen and oxygen. These elements chemically react to create water, which has distinct characteristics not found in either hydrogen or oxygen alone. This bond can be ionic or covalent depending on the elements involved, but the key point is that the bonding creates a new substance with specific chemical identity and properties.

The other options describe different types of substances or arrangements that do not fully capture the definition of a compound. For instance, substances containing elements that are not chemically bonded represent mixtures rather than compounds.