**Explanation:**

When a bank returns a cheque, it means that the cheque has been rejected and will not be honored for payment. In this case, the bank has returned a cheque of Rs. 9900 that was received from Kulu and Sons in settlement of an account of Rs. 10000. This transaction needs to be recorded in the cash book.

**Recording in the Cash Book:**

To record this transaction in the cash book, we need to consider the following points:

1. **Date:** Write down the date on which the cheque was returned by the bank.

2. **Particulars:** In the "Particulars" column, write "Bank" to indicate that the transaction involves the bank.

3. **L.F. (Ledger Folio):** Leave this column blank for now.

4. **Amount:** In the "Amount" column, write the amount of the cheque that was returned, which is Rs. 9900.

5. **Debit/Credit:** Since the cheque was returned by the bank, it means that the bank account has been debited. Write "By" in the "Debit" column.

6. **Date:** Write down the date on which the cheque was originally received from Kulu and Sons.

7. **Particulars:** In the "Particulars" column, write "Kulu and Sons" to indicate the name of the party from whom the cheque was received.

8. **L.F. (Ledger Folio):** Leave this column blank for now.

9. **Amount:** In the "Amount" column, write the amount of the cheque that was originally received, which is Rs. 10000.

10. **Debit/Credit:** Since the cheque was returned, it means that the account of Kulu and Sons needs to be credited. Write "To" in the "Credit" column.

11. **Narration:** In the "Narration" column, write a brief description of the transaction, such as "Cheque returned by the bank."

12. **Balances:** Update the bank and Kulu and Sons' accounts in the respective balance columns.

By following these steps, the transaction of the bank returning a cheque of Rs. 9900 received from Kulu and Sons in settlement of an account of Rs. 10000 can be properly recorded in the cash book.