Greetings of the day!!!
Very valid questions
1. What does Immediate Effect actually means?
Ans: As per rule company should give you one month notice but in your case, you should not report to duty from the time of receiving the notice but you are entitled to one month salary.
2. Does the company have the right to refuse me an NOC (release)?
Ans: As per current rule, your company has full right to refuse.
3. Do I still have to hand over my jobs and responsibilities in a given or specific time?