Answer;
2) the rate at which changes occur in a type of molecule
Explanation;
The molecular clock is figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged.
Scientists can use relaxed-clock methods to deal with variation in the rate of the molecular clock. By measuring the patterns of evolutionary rate variation among organisms, they can also gain valuable insight into the biological processes that determine how quickly the molecular clock ticks.
