Question

What takes up most of the volume of an atom?

Answer 1

An atom is the smallest unit of any molecule which retains its all chemical properties. Atom is further divided into sub-atomic particles which are protons, neutrons and electrons. Protons are positively charged ions, electrons are negatively charged ions and neutrons are neutral subatomic particles.

Complete answer:
Dalton in $1810$ proposed that all matter is made of atoms that are indivisible i.e., atoms can’t be sub-divided into sub-atomic particles. But Rutherford in $1911$ gave postulates on atomic theory which concluded that atoms are further divided into three subatomic particles that are protons, neutrons and electrons.
According to Rutherford atomic model, following observations were concluded:
Most of the mass of an atom is concentrated in a very small region called the nucleus. It consists of protons which are positively charged particles and neutrons which are neutral.
Hence for an atom, Number of protons $+$ Number of neutrons $=$ Mass number of the atom
Nucleus of the atom is surrounded by electrons which are negatively charged particles and they revolve around the nucleus in a fixed circular path called orbits.
The overall atom is electrically neutral because the number of protons is equal to the number of electrons. So, the positive charge of protons completely counter-balance the negative charge of the electrons.
Most of the mass of an atom is concentrated in its nucleus but most of the volume of an atom is taken from the empty space between the nucleus and the orbits of electrons. In other words, most of the volume of an atom is occupied by electron clouds of an atom

Note:
Electron cloud here refers to the area between the nucleus and orbitals in which the probability of finding electrons is maximum. The area of an electron cloud is densest if it has high chances of finding electrons.