Naveen,
Yes, you'll be eligible to get into any IITs and NITs after repeating your 12th board. But, if you are doing your 12th through CBSC and ISC boards you have to score a minimum of 75% in total. If you're doing your 12th board from any other state boards than you have to be within the top 20 percentile to be eligible to do so.
Hope this helps!
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