Give one advantage and one disadvantage of laboratory experiments.

A question like this is likely to be worth 2-4 marks. In order to answer the question fully, you will need to state the advantage or disadvantage and then explain your reasoning.

An advantage of laboratory experiements are that they allow the experimenter to have greater control over the variables which increase reliabiity because you can be more confident that the independent variable is the only factor influencing the dependent variable. 

A disadvantage of laboratory experiments are demand characteristics. The participants may be aware that they are participating in an experiment and therefore may behave differently to how they would typically behave. This reduces the validity of the study.