Answer:
The correct option is D.
Explanation:
It is given that the population of bacteria begins with 1 bacterium and triples every hour.
Let initial population be 1.

The population of bacteria after 1 hour is

The population of bacteria after 2 hour is

Similarly the population of bacteria after n hour is

If x is number of hours and y is the population of bacteria after x hour, then

The other way to find the population model is shown below.
The population model is defined as

Where, a is initial population and (1+b) is growth factor.
In the given situation the initial population is 1 and growth factor is 3, therefore

Therefore option D is correct.