Iron-56 is a very stable nucleus while cobalt-60 is an unstable nucleus. Which nucleus would you expect to have more binding energy per nucleon?

The minimum energy which is needed to deconstruct the nucleus of an atom into its components i. e. neutrons, protons is said to be nuclear binding energy.

Binding energy per nucleon is equal to the ratio of binding energy to the total number of protons and neutrons. Since, with increase in binding energy per nucleon, there will be increase in stability or vice-versa.

Now, according to binding energy per nucleon curve, iron-56 is the most stable nucleus as it has highest binding energy per nucleon (binding energy per nucleon attains maximum when number of nucleons i. e. protons plus neutrons is 56) and the smaller and larger nuclei than iron-56 has less binding energy per nucleon. Therefore, cobalt-60 is an unstable nucleus as it has less binding energy per nucleon in comparison to iron-56.