After 10th class to complete 12th class you require minimum two years. There is a gap of one year. That means you passed 12th class after 3 years of your 10th class passing. Am I correct?
In such case, you will not have any problem to attend NEET exam. The education qualification for NEET is as given below.
Candidates must have passed the higher/senior secondary examination or ISCE which is equivalent to 10+2 examination Higher/Senior Secondary Examination after a period of 12 years study.
Candidates must pass the above qualifying examination with Physics, Chemistry, Biology/Biotechnology and English subjects.
Candidates must secure minimum 50% marks (GEN), 40% marks (SC/ST/OBC), 45% marks (GEN PH) & 40% marks (SC-PH/ST-PH/OBC-PH) taken together in PCB subjects.
Candidates who are in the 12th standard can also apply. They must have to show the passing certificates complying with the percentage criteria at the time of first round of counselling.
If you are fulfilling the above then one year gap is not a problem.
For IITs, one year gap is not an issue provided you fulfil all other criteria.