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select the correct answer from each drop-down menu.
, and the outer part of the
much of the mass of an atom is concentrated in its nucleus. the nucleus contains
atom contains

neutrons and electrons

protons and electrons
protons and neutrons

protons and neutrons

Explanation:

An atom is said to be the simple units of matter and basic of describing elements structure. An atom of an element have protons , neutrons and electrons.

The protons and neutrons of an atom are usually located in the nucleus of an atom. The sum of the proton and neutron of an atom determines the atomic mass of an element. This means the proton and neutron plays a major role in determining the mass of an atom. The proton is usually positively charge and tends to repel each other in the nucleus of an atom. The neutron has no charge but usually possess more weight than the proton.

The electron is located at the outer parts of the atom. it usually revolve round the atom . The electron determines how the atoms of an elements bond with other atoms. For an electronic neutral charge of any atom the proton number is equal to the electron number.  

The picture above illustrate how the proton, neutron and electron reside in the atom.