There is no fixed format per se for a Gap year certificate. It should be done as an affidavit on a stamp paper. But you can use this for reference: https://gcoeara.ac.in/admission/AY2018-19/GAP%20Certificate%20Affidavit.pdf or https://www.lpu.in/AnnouncementPanel/Upload/lpude/AFFIDAVIT_FOR_GAP_PERIOD.pdf .
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