Question

What characteristic property of nuclear force explains the constancy of binding energy per nucleon (BE/A) in the range of mass number ‘A’ lying 30 < A < 170?

Answer 1

The approximate constancy of BE/A over most of the range is saturation property of nuclear force,

In heavy nuclei: nuclear size > range of nuclear force.

So, a nuclear sense approximately a constant number of neighbours and thus, the nuclear BE/A levels off at high A. This is saturation of the nuclear force.