If edcation institution or university formed solely for education purpose and not for profit and does not have annual receipt in excess of Rs. 1 crore (rule 2bc), than it is exempt from income tax under section 10(23c) (iiid) and (iiie).
If exceeds more than one crore than it may give application in form 56d to chief commissioner or Director General of Income tax for exemption.
Only trust or society claming exemption under section 11 and 12 ( it may be education insitution also) need to register under section 12A for which it has to give application in form 10A to commissioner of income tax. Commissioner will ask for document i.e society registration copy and member name id proof and address proof, memorandum of association etc).
It means you can avail option of your choice but in case first it will be only for education purpose and in second case your are of social work will be wide and no limit also.