is the energy required to assemble a nucleus or
to separate the nucleus into its individual components/nucleons. (d)
The binding energy per nucleon is the total binding energy for a particular nucleus divided by the number of nucleons contained in the nucleus.
For energy to be released in a nuclear reaction, fusion or fission, the binding energy must increase.
Image taken from http://www.smsec.com/en/nucl/07_1.htm