Question

What is the most basic unit of matter?

Answer 1

Hint :We know that the Greek philosopher Democritus discovered the idea for the atom. Although, the idea was not recognized for more than $2000$ years. John Dalton re-introduced the concept of atom in $1800.$ In the nucleus of an atom only the positive charge and another one which is neutral are present. Nucleus contains positively charged particles and no charged particles.

Complete Step By Step Answer:
An Atom is the smallest unit of matter (Anything that has mass and occupies some space).every state (solid, liquid, gas, and plasma) is composed of neutral or ionized atoms. Every atom is composed of a nucleus and that nucleus consists of charge particle protons and neutral particles neutrons. Atoms are extremely small, typically around $100$ picometre. Protons and neutrons in the nucleus are collectively called nucleons. Democritus was the first who introduced the concept of atom but the first accurate and precise theory which gives us the proper explanation of an atom is ‘Dalton’s atomic theory’.
Atoms are the building blocks of matter because they cannot be "broken down" further by chemical means (although we can split them). Inside an atom consists of three different particles: protons, neutrons, and electrons. Protons carry $a+1$ positive charge and have a mass of $1amu.$ Neutrons carry no charge and also have a mass of $1amu.$
Electrons carry a $-1$ negative charge and have a mass of ${\displaystyle \frac{1}{1836}}amu$
 $\therefore 1amu=1.66\times {10}^{-27}kg$
Inside of a proton are three quarks. Electrons are in a family called leptons and they are not made up of quarks.

Note :
Remember that as time passes, many theories were given but no one was accurate because now there are many experimental proofs that particles like proton, electron, meson, neutron, positron, neutrino, etc. are embedded in an atom. Also remember that hydrogen is the only element which has no neutrons