Dear candidate, you have not mentioned which merit you are talking about. First of all a percentage is calculated by adding marks of all subjects and dividing it by total number of marks of all subjects and multiplying it by 100. Then it depends how many students are in that merit. If the merit is of school, then the person getting the highest rank will be at the top of the merit list. If merit is about taking admission in a particular college, then out of the number of students who have applied, the person with the maximum percentage will be at the top of the list. Some colleges ask only for the score of the best 4 subjects. It is not mandatory that merit is based on all subjects. Some colleges calculate merit through percentile or cgpa method which is totally dependent on number of students appearing. The person with maximum percentile or cgpa will be at the top of merit list.

Hope, it helps!