Define isotope and how isotope are formed?

Isotopes are chemical elements that have the same number of protons in the nucleus, but a different number of neutrons.

Any of two or more forms of a chemical element, having the same number of protons in the nucleus, or the same atomic number, but having different numbers of neutrons in the nucleus, or different...

The mass number is the total weight of neutrons and protons in the nucleus of an atom.

Isotopes are formed either naturally through radioactive decay of elements or artificially through element irradiation by particles as neutrons, protons, electrons, or alpha particles in accelerators...

radiates either alpha beta or gamma radiation, in order to go to a more stable state