Trout are a type of fish that live in freshwater ponds and streams. Raychelle did an investigation to see how the amount of nitrogen in pond water affects the number of trout in the water. She tested the water of 20 different ponds in her city. Each one had a different amount of nitrogen in it. She then did a study to determine the number of trout in each pond. She compared the amount of nitrogen to the number of trout in each pond. What was Raychelle's dependent variable?

A scientific experiment is designed in a way that it tests the hypothesis and contains three different types of variables: the independent variable (which can be manipulated), dependent variable (which is tested in the experiment) and constant ( which is kept same throughout the experiment).

In the given question, since the researcher wants to study the effect of nitrogen on the number of trouts in which the variable to be studied is the number of trout which depend on the concentration of nitrogen in water bodies.

Thus, a number of trout in ponds is the correct answer.