CBSE Class 12-science Answered

For light nuclei the most stable mixture is about 50-50, but stable heavy nuclei have two or three times more neutrons than protons.

So the above statement that the number of neutrons is more than the number of protons, in heavy nucleus, is true.

This is because the electrical repulsions of all the protons in a heavy nucleus add up to a powerful force that would tend to tear it apart. The presence of a large number of neutrons increases the distances among the protons, and also increases the number of attractions due to the strong nuclear force.