The basic unit for an element is atom, whereas the basic unit for the compound is molecule.

Hint: Matter: Matter is everything that occupies space and has mass. All physical objects are composed of matter. The classical states of matter are- solid, liquid and gas. Solids have definite shape and volume. Liquid has definite volume but not shape. Gas neither has a definite volume or shape.

Complete step-by-step solution:
Matter is very important in chemistry so that’s why we need the classification of matter.
Elements
Compounds
Mixtures.
Elements: A species of atoms that have the same number of protons in their atomic nuclei. Although an element has the same number of protons in their nuclei but different number of neutrons in nuclei. So the mass of the elements varies. Atoms are the smallest unit of elements. Elements are arranged in periodic tables upon their groups. Elements either metallic or non-metallic. They placed in their respective block. Metals are classified as main metal, transition metal and f-block metals. Elements consist of individual atoms. Each element always consists of the same type of atoms that show the same property. So the basic unit of an element is atom.
Compounds: When two or more elements chemically combine in a fixed ratio by mass, the obtained product is known as compound. The compound consists of the smallest unit which contains at least two different types of atoms joined together by chemical bond. When the elements are combined some of their properties are lost and the newly formed compound has new properties. Compounds are always represented by chemical formulas. So the basic unit of compound is molecule.

Note: Mixture is a material made up of two or more different substances which are not chemically combined. A mixture is a physical combination of two or more than two substances. Mixtures can be classified in two types- homogenous mixture and heterogeneous mixture. Mixtures mixed in the form of solutions, suspensions, and colloids.