Which of the following characterizes nuclear reactions?
the loss of mass cannot be accounted for.
the chemical composition of the atoms remains the same.
the number of protons and neutrons in reacting atoms changes.
energy is not conserved.

The number of protons and neutrons in reacting atoms changes.

Explanation:

Typical of all nuclear reactions is the change that occurs within the nucleus of the atom. In a nuclear reaction, the number of protons and neutrons changes to form a new atom.

What drives a nuclear reaction is the stability ratio between the neutron and protons. Every atom has its stability ratio. A nucleus with a neutron/proton combination different from the stability ratio will be unstable and split into one or more other nuclei. Therefore, a nuclear reaction occurs to maintain and ensure that the stability ratio is maintained and achieved.

the electrical  conductivity  of asolution  of an electrolyte is measured by determining the resistance of thesolution  between two flat or cylindrical electrodes separated by a fixed distance.