See explanation below.
Work Step by Step
he stability of a nuclide is determined from the ratio of number of neutrons to protons that is N/Z ratio. If N/Z ratio is either too high or too small then the nuclide is unstable a.N/z ratio of nuclide a is 1.4, hence it is stable. b.N/z ratio of nuclide b is 1.4, hence it is stable. c.N/z ratio of nuclide c is 1.1, hence it is unstable.