The stability of an isotope is based on its

(1) number of neutrons, only

(2) number of protons, only

(3) ratio of neutrons to protons

(4) ratio of electrons to protons

Answer=3

The ratio of neutrons to protons generally determine the stability of an isotope.

Answer is (3) - ratio of neutrons to protons.

Isotopes are the atoms which have same atomic number but have different number of neutrons of same element.

Atomic nucleus can be stable or unstable. The stability of isotopes is based on neutron / proton ratio. Unstable nucleus tries to become stable by emitting radiations.