To determine if an instrument qualifies as a Promissory Note, specific essential requirements must be met. Let's analyze the given options against these requirements.

Promissory Note Essential Requirements

An instrument is considered a Promissory Note if it meets the following criteria:

• It must be in writing.
• It must contain an express promise to pay a certain sum of money.
• The promise must be unconditional.
• It must be signed by the person making the promise (the maker).
• The sum payable must be a certain sum of money.
• It must be payable either on demand or at a fixed or determinable future time.
• It must be payable to a specified person or to the bearer of the instrument.

Analysis of Options

Let's evaluate each option provided:

• Option 1: The instrument must contain a promise to pay. This is a fundamental requirement. A promissory note fundamentally involves a promise.
• Option 2: A mere acknowledgement of indebtedness is sufficient. This is not sufficient. While acknowledging a debt might be part of the context, a promissory note specifically requires an explicit promise to pay, not just an admission of owing money.
• Option 3: The sum of money to be paid must be certain. This is essential. The note must clearly state the exact amount to be paid.
• Option 4: Promise to pay must be unconditional. The promise to pay should not be subject to any uncertain future conditions.

Conclusion

Based on the essential requirements, a mere acknowledgement of indebtedness is not enough to make an instrument a Promissory Note. An explicit and unconditional promise to pay a certain sum is required.

Therefore, the statement that is not an essential requirement is that a mere acknowledgement of indebtedness is sufficient.