Paper 3 is split into Section A and Section B. Section A has a lot of questions on practical techniques and skills. In this section, one of the questions is given for critical analysis of experimental data. Basically, you'll get some data in a graph or a table and be asked to draw conclusions from it. You could also be given a conclusion and asked to evaluate how well the data supports the conclusion.
Similar to Paper 1 and 2 though, there will be fact recall questions and ones that test for application and calculation questions. Essentially, you need to be really good on the content as well as the exams. Section B of this paper has a 25 mark essay question.