Describe the relationship between the amount of C-15 and time?

As time increases, C-15 (Carbon) decreases. During radioactive decay, the amount of Carbon in a substance undergoes half-lives (A sample could have  a half life of 1002 years, for example.) When that substance ages to that timeframe, it loses half of its mass. Then for the next half-life, it loses half of that new mass, and so on.

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.