Question

a piece of sodium metal can be described as a pure substance and a compound. an impure substance that is reactive. an impure substance that is unreactive. a pure substance and an element.

Explanation:

• A pure substance has a definite composition. Sodium metal (\(Na\)) has a definite composition (only sodium atoms), so it is a pure substance.
• A compound is made of two or more different elements chemically combined. Sodium metal is made of only one type of element (sodium), so it is not a compound.
• Sodium metal is not an impure substance. Impure substances (mixtures) have variable composition.
• Sodium metal is very reactive (e.g., reacts with water: \(2Na + 2H_2O=2NaOH + H_2\uparrow\)). But the key classification here is based on pure - substance/element vs compound/mixture. Since it is a pure substance (definite composition) and an element (only one type of atom, \(Na\) atoms).

Answer:

a pure substance and an element.