What is is the average mass of a proton or a neutron? a) 1 amu b) 2 amu c) 3amu d) 4 amu

The answer is a) 1 amu

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

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.