Neutron-Proton Ratio and Nuclear Stability

Most naturally occurring nuclides hav even numbers of neutrons and even numbers of protons. Nuclides with odd numbers of both neutrons and protons are least common and those with odd-even combinations are intermediate in abundance.
No. of protons even even odd odd
No. of neutrons even even even odd
No. of stable nuclides 157 52 50 5
A plot of the number of neutrons versus the number of protons shws that as the atomic number increases, the N/P ratio of the stable nuclides increases.