what are the prerequisite for installing oracle 11gr2
Check this out:
[https://docs.oracle.com/cd/E11882_01/install.112/e47798/reqs.htm#NTDBI002][1]
[http://docs.oracle.com/cd/B28359_01/install.111/b32006/reqs.htm][2]
Probably you will get answers for such questions quickly if you google them.