The total negative charge of all the electrons outside the nucleus is equal to the total positive charge of all the protons inside the nucleus. This makes the atoms electrically neutral. That is, nuclear charge is the total charge of the protons only. Therefore, neutrons are called as neutral particles.

The number of electrons or protons is an atom is called the atomic number (Z) of an atom.

An atom is the smallest particle of a chemical element that retains its chemical properties.

Sub-atomic particles:
(i) Proton (p): This is the positively charged particle and it is located at the nucleus.
(ii) Neutron (n): Neutron is inside the nucleus. The neutron does not have any charge. Except hydrogen (protium), the nucleus of all atoms contain neutrons.
(iii) Electron(e): This is a negatively charged particle. Electrons revolve around the nucleus of the atom in specific orbits.

(i) Yes, an atom of an element has no electron will have the mass.
(ii) (Atomic mass, only depends on the mrmber of protons and the number of neutrons inside the nucleus. It is independent of number of electrons.)
(iii) Atom can exist with out electron and becomes a cation.
Ex: 
1) Hydrogen atoms (Z = 1) has only one electrons.
2) It loses one electron and becomes H⁺ ion
3) H → H⁺ + 1e^-
  (atom)    (Ion)