Which is a characteristic of the part of the atom marked a

Option (a)

An atom of element has there subatomic particles namely, proton, electron and neutron. Here, for a neutral atom, number of proton is equal to number of electron (this is not in the case of ions), this is equal to atomic number of an atom. In an atom, nucleus contains protons and neutrons which is responsible for mass of the atom and electrons move around nucleus in fixed orbits. Thus, atomic mass of an atom is equal to sum of number of protons and neutrons.

The part of atom marked A here is nucleus which contains protons and nucleus. It is not negatively charged because it has protons which are positively charged particles and neutrons which are neutral. The space is not empty because the size of the nucleus is very small and it has almost all the mass of the atom and it does not contain electrons because electrons revolve around nucleus in fixed energy shells.

Since, almost all of the mass of an atom is in its nucleus thus, the characteristic of part marked A is that it is very dense.

Therefore, option (a) is correct.

a polar bond is formed when electrons are shared unevenly between atoms