How do you determine isotope stability?

Hint:The isotopes are the substances which tend to contain the same number of the protons as well as the electrons but the different number of the neutrons. This results in the formation of the two isotopes which are of the same element but with different atomic weight and moles. The isotopes of the carbon are carbon 12, carbon 13 and carbon 14.

Complete step-by-step answer:So for the determination of the isotope stability we need the total number of the nucleonsor the neutron proton ratio. The main or the principal factor for isotope determination is the ratio of neutron and proton. At close distances we observe a strong force of nucleus or the nuclear force is present between the nucleons. This force of attraction comes due to neutrons. So if the more number of protons are present in the nucleus then more numbers of the neutrons are needed for binding the nucleus together. When the nucleus gets bigger the electrostatic force of repulsion present between the protons gets weaker. This nuclear force is 100 times approximately stronger than that of the electrostatic repulsions. After attaining a certain size the strong force does not tend to hold the nucleus together. If extra neutrons are added the space present between the protons gets increased. This tends to decrease their repulsion if the number of neutrons are more than the nucleus get out of balance and decay. The belt of stability determines the ratio of protons to neutrons. For the atoms which have 20 protons or less the ratio for them is generally 1:1. When the atoms grow larger the ratio gets shifted slightly more towards the neutrons than neutrons. So the isotope should have mostly approximately a 1:1 ratio of proton to neutral to be stable.

Note:There are other terms such as isotones which are defined as the atoms which have the same number of neutrons. Whereas in isoelectronic the atoms tend to have the same number of the electrons. The isobars are the atoms which have the same mass number but the atomic number is different.