Answer:
Null hypothesis: the behavior of mosquito larvae doesn't change in the presence/absence of predators added to the tanks in Treatments 2 and 3.
Explanation:
In statistics, the null hypothesis states that there are no differences between the two variables tested in the experiment, while the alternative hypothesis uses the experimental data in order to reject the null hypothesis. In this case, the alternative hypothesis will use the data from treatments 2 and 3 to confirm that predators can modify the behavior of mosquito larvae.