Applying wrong model

If they ask you to apply a specific model and you don't, then you are in trouble. However, if no specific model is specified you can use which ever you want to. Your choice should depend on what's in the question: which model could the data in the question be fitted to?

So, if no specific model is require, however i did not write out the model that the examiner wish us to apply, i still can gain full mark?

Yes you could. However, if you use in model that does not fit very well you might not be able to say as much as you could have with a more appropriate model. Remember also that sometimes more than one model can be used in your answer, especially in the 50 mark question, but don't bring in too many otherwise you will refer to lots of models without solving the question. In the exam you will obviously not see the examiner's answer so will not know if the examiner was thinking about something different. Therefore, it is important to have the self confidence that what you are doing is correct and to write the very best answer you can using whatever approach you have chosen: be confident that you are right. Good luck in the exam!

Ok, Thank you very much sir! :D