Classify the following substance as element, compound or mixture:

Oxygen

Element: An element is a pure substance that cannot be split into simpler substances.

• Example: Hydrogen $\left({\mathrm{H}}_2\right)$, Copper $\left(\mathrm{Cu}\right)$ etc.

Compound: A compound is a pure substance in which different elements combine chemically in a fixed composition to give a compound.

• They can be broken down into elements that make up the compound by using chemical or electrochemical methods.
• The properties of the compound are entirely different from the elements from which it is formed.
• Example: Water $\left({\mathrm{H}}_2\mathrm{O}\right)$, Common salt i.e.; Sodium chloride $\left(\mathrm{NaCl}\right)$

Mixture: When two or more substances (elements or compounds or an element and compound) are mixed in any proportion.

• The components of a mixture can be separated by physical methods of separation.
• Example: A mixture of Sand and Oxygen $\left(\mathrm{Fe}\right)$ can be separated by the use of a magnet (physical process) where Oxygen gets attracted to the magnet leaving behind the sand.

Oxygen $\left({\mathrm{O}}_2\right)$ can be classified as an element.

• This is because Oxygen is made up of Oxygen particles (i.e.; molecules) only.
• As Oxygen $\left(\mathrm{O}\right)$ atoms are unstable, therefore they combine to exist as molecules $\left({\mathrm{O}}_2\right)$.
• Oxygen contains only one type of constituent particle i.e.; Oxygen molecules, therefore it is a pure substance.