In a multiple-choice exam, you simply pick an answer from the available options. There is a single correct answer and there is no room for interpretation. Many multiple-choice questions are structured in a way that is designed to trip you up. On the surface there is more than one possible correct answer. Elimination is often the only strategy that can reliably get you to the correct answer:
If the exam is assessed using negative marking, it will not always be in your favour to pick an answer at random.
I have taken several multiple-choice exams where a correct answer would gain 5 marks and an incorrect answer would lose 2 marks. This would be out of a choice of 5 answers.
If I chose an answer at random, I would pick the correct answer 1 in 5 times. 4 in 5 times I would pick the wrong answer. So 20% of the time I would gain 5 marks, and 80% of the time I would lose 2 marks.
If you have eliminated enough answers to make the average outcome positive (in this case you would need to eliminate 2 out of 5 answers), then it makes sense to choose one of the remaining answers at random.
Some exam types will use a gentle form of negative marking. For example, science exams often contain questions such as “List 3 Properties of Metals”. In this case the question would be worth 3 marks. If you list more than 3 properties, marks will be deducted for wrong answers. If you list 5 properties and 2 of them are wrong then you will lose 2 marks, even though you listed 3 correct properties. If all 5 properties are correct, then you still only get 3 marks.
This means that you can never benefit by doing more than you are asked for. Resist the temptation.
However, in this situation you will never lose marks for attempting to answer the question. So if you listed 3 incorrect properties, you would score 0, not -3.
Remember: if you know that an exam is not negatively marked, there is never a reason to leave any answer blank. Even if you have no clue how to answer a question, you have a better chance of getting it right by writing something than nothing at all.