NOC and its importance

Sir/Madam, I am working in an Insurance company PSU. I work as clerk/assistant ie. Grade C. I am trying to get other Government Job in Central/State Government. I have to give every exam with at-most care to get good results and selection. As a clerk/assistant i do not hold any position which have decision making ability or actions or signing authority. We have rule to give NOC 3 times in a Year. I have following question... 1.) The Exams has stated that NOC is mandatory. If i do not take NOC for the government exam and if get selected in that job what to do in such case so that i can get the job without NOC, i will resign from my old company without any second thought? 2.) I will not hide my previous PSU job details to the Panel , and what should i do so that the conditions which are fulfilled through NOC are fulfilled be me? 3.) What to do when, i am unable to provide with NOC as restriction is there for 3 NOC exam in a year only.? 4.) Why NOC is needed...so that i can fulfill all conditions without problems and join the new government organisation.? Thankyou...