Hello Preeti,

Originally you should've been eligible for NEET considering that the eligibility for unreserved category is 50% and for the reserved categories is 40%. Of course this can be cancelled in case you have not passed any subject out of the three sciences - Biology, Chemistry or Physics separately or if you don't meet the age criteria of the same. In case of the subjects you should give the retest for only the subject you did not pass unless of course you would like to increase your percentile for which you can go for retest of other subjects, totally upto you. 

Hope this helped.

No , Preeti i am afraid it doesnt work like that , if at all you want to give an improvement and apply for NEET , it has to be for ALL THE SUBJECTS . Had it been just to improve your marks in a particular subject it wouldn't have been much of a problem , but when the question of eligibility comes its all the subjects that you have to appear .

All the best .