i failed in 2nd pu but i want to write nata can i write?

Hello,
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To get eligible for NATA examination you should be cleared with 12 with maths compulsory subject without any backlogs. Unless you clear you backlogs you aren't eligible for NATA examination. So, first clear your backlogs.
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Now, what do you  mean by PU? are you asking about Punjab university? Please let us know if the above information is not helpful with further information. We will help you out