Hello sumittamrakar,

Hope you are doing well, Now coming back to the question as we know

An atom is a particle of matter that characterizes a chemical element. It is the smallest part of ordinary matter. It is made from particles called protons, neutrons and electrons called the subatomic particles.

An element is a substance that is made entirely of one type of atom. For example, the element sodium is made up of only sodium atoms.

A molecule is a substance that contains two or more atoms chemically joined, such as H2,O2

A compound is a substance that is made up of two or more different elements (https://socratic.org/chemistry/a-first-introduction-to-matter/elements) that are chemically joined, such as H2O,CO,NaCl .

hope this will help you a lot,

thank you.

hey,

atoms are smallest and simplest unit of matter , it is made up of protons , neutrons and electons known as subatomic particles

molecules are the substance that contains two or more atoms chemically joined

and a compound is a substance which is composed of two or more different elements that are chemically joined

in short atoms are made up of subatomic particles , molecules are made up of atoms and compound are made up of molecules .

hope this helps!