Each of the experiments presented in the unit is based on the so-called engaging questions. A teacher should guide a discussion in such a way, that students will define the research problem, which forms the basis of presented experiments, by themselves. Experiments III.3, IV.2, IV.3b are open inquiry kind. Exemplary approaches for solving these problems as well as exemplary results are included. Due to the fact, that students should design the procedure for the experiment by themselves, the outcome may strongly depend on the chosen method.