Important Ones:
http://gateoverflow.in/questions/operating-system?sort=featured
Some Extra Questions
https://wps.prenhall.com/br_deitel_sistemas_3/39/10059/2575352.cw/index.html
OS: http://www.cse.iitb.ac.in/~krithi/courses/684/osquiz0.pdf
Virtual Memory: http://www.cs.utexas.edu/~lorenzo/corsi/cs372/06F/hw/3sol.html
Suggest me best material for Operating system...