Ryan is conducting an observational study on human behavior in different environments. Which of these sample sizes will probably help him arrive at the most accurate conclusion?

This is the case of Inductive Arguments. In logic, inductive arguments are all about the content of the premises and involve probability. Logicians focus on the strength of this type of argument. In a strong inductive argument, if the premises are assumed true, it is likely that the conclusion is true, it does not mean that it must be true, it is possible that the conclusion could be false. Thus, if the conclusion is likely to not be true based on the assumed truth of the premises, the inductive argument is weak.

While there are mathematical ways to determine probability, most of the time you'll have to use your intuition and experience to help you figure out whether an inductive argument is strong or weak.

So according to this, given that Ryan is conducting an observational study on human behavior in different environments. To get the most accurate conclusion he needs to get the greatest sample size, that is 50 Individuals.