Procedure to close CGAS account

To close CGAS account opened with bank, Form G is required.
My queries are
1. How much copies of Form G are to be submitted to IT accessing officer for approval?
2. Which documents are required to be attached with Form G? How much sets?
3. The return ITR2 was approved by CPC, and no tax was demanded. Can accessing officer challenge the order/intimation passed u/s 143(1)?