Explanation:

- Option 1, conditional: A promissory note with a condition means payment relies on an event or action. This is not typical for standard promissory notes.

- Option 2, unconditional: This is the correct choice. Promissory notes generally promise payment without any conditions, making them straightforward financial instruments.

- Option 3, maybe conditional or unconditional depending upon the circumstances: While some financial agreements can be conditional, promissory notes are typically not designed this way, as they should guarantee payment without reliance on other factors.

- Option 4, none of the above: This isn't applicable, as option 2 covers the standard nature of promissory notes.