Quick questions on Mixtures, elements and compounds: N(A)-Level Chemistry

An element is a substance made of only one type of atom. It cannot be broken down into anything simpler by chemical means. There are over a hundred elements, listed in the Periodic Table, such as oxygen, copper, and carbon. Each has its own symbol, such as $\text{O}$, $\text{Cu}$, and $\text{C}$.

A compound is a substance made of two or more different elements chemically combined in a fixed ratio. The atoms are joined by chemical bonds, and the compound has its own new properties that are different from the elements it is made from. Examples are water, $\text{H}_2\text{O}$, carbon dioxide, $\text{CO}_2$, and sodium chloride, $\text{NaCl}$.

A mixture contains two or more substances that are simply mixed together but not chemically combined. The parts keep their own properties and can be separated by physical methods such as filtering or distilling. Air, sea water, and a mixture of iron and sulfur powders are all mixtures.

State whether each of the following is an element, a compound, or a mixture: copper, carbon dioxide, air. [3 marks]

Explain why oxygen gas, $\text{O}_2$, is described as an element but is made of molecules. [2 marks]

Give two differences between a compound and a mixture of the same two elements. [2 marks]