ITC for mixed supply

In case of rice mill they have ITC on consumables, Services, fixed assets and purchases also.

my questions are:

1. Whether the credit reversal under rule 42 and 43 apply and need to be done on monthly basis??

2. In case where only exempted supply is there in a month and during such month ITC of consumable was there which was used for both taxable as well as exempt supplies however during the month taxable supplies was nil. then how to take credit of the same.

3. In a month sale was completely nil neither exempted nor taxable supplies made during the month but common credit was there. in that case how to claim such ITC.

4. In case of services like repair maintenance services, bank charges how to compute elegilbe ITC and amt of ITC reversal.

please clarify and thanks in advance.🙏