Hi Gaurav,
Hope you are doing all good. Your question is incomplete as you have not mentioned any specific exam. Unless mentioned, no specific answer can be given.
However, in general, there are exams that you can attempt infinite number of times while some exams can be attempted for a limited time. For example JEE Advanced can be attempted twice. Once, on the year you pass your 12th and once the following year, failing to which you are not given any more chance. Again there are certain exams, that allows you numerous attempts.
So, specify the exam you are curious about, so as to get a particular answer.
Hope this helps.
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