A transaction that would cause the cash book balance to be less than the bank statement balance is
Answer Details
An unpresented cheque is a transaction that would cause the cash book balance to be less than the bank statement balance. This occurs when you have written a cheque but the recipient has not yet deposited it into their bank account, and therefore it has not yet been processed by your bank.
When you reconcile your cash book (which records all your transactions) with your bank statement, you may have recorded the cheque in your cash book, but it has not yet appeared in your bank statement. This means that your cash book balance will be higher than your bank statement balance.
For example, if you wrote a cheque for $50 to pay a supplier, and they have not yet deposited it into their bank account, your cash book will show a decrease of $50, but your bank statement will not reflect this decrease until the cheque is deposited and processed by the bank.
Therefore, if you have unpresented cheques in your cash book, your cash book balance will be higher than your bank statement balance, and this will cause a difference between the two balances.