Explanation:

- Option 1: Promissory Note

- It is a written promise to pay a certain sum of money on demand or at a future date.

- In the context of the Negotiable Instruments Act, a promissory note is a key financial instrument but is not addressed in Section 6.

- Option 2: Bill of Exchange

- It is an order by the drawer to the drawee to pay a specified sum to a third party.

- Like a promissory note, it’s significant under the Act but not covered in Section 6.

- Option 3: Cheque

- A cheque is a bill of exchange drawn on a specified banker and payable on demand.

- Section 6 of the Negotiable Instruments Act, 1881 (not 1880) defines a cheque.

- Correct Answer

- Option 4: None of the above

- Since a cheque is defined under Section 6, this option is incorrect.