An electron is a particle with a negative charge, found in the nucleus negative charge, found outside the nucleus positive charge, found in the nucleus positive charge, found outside the nucleus

An electron is a particle with a negative charge, found outside the nucleus.

Explanation: In an atom, there is a nucleus in the center that has protons and neutrons. Mostly the mass of an atom is the sum of masses of protons and neutrons.  Protons are positively charged ions and neutrons are neutral.

Electrons are present around the nucleus(outside the nucleus) in different energy shells. An electron has negative charge and gain or loss of electrons is the cause of chemical reactions.

Number of protons equals to the atomic number of an atom. Number of electrons is also same to the number of protons for a neutral atom where as the difference of mass number and protons is the number of neutrons.