Which of the following is not a method by which a state may express its consent to be bound by a particular treaty:-

Consent by verbal assurance of Head of State

The correct answer is Option (3) → Consent by verbal assurance of Head of State

Consent by Verbal Assurance of Head of State: While the verbal assurance of a Head of State may indicate a willingness to support a treaty, it does not constitute a formal method of expressing consent to be bound by a treaty. Legal obligations typically require documented actions like signing or ratifying, rather than verbal assurances.

• Consent by Signature: A state can express its consent to a treaty by signing it, which indicates preliminary acceptance but may require further action (like ratification) to become legally binding.

• Consent by Exchange of Instruments: This method involves the formal exchange of documents (instruments) that constitute the treaty, representing consent by both parties.

• Consent by Ratification: This is the formal confirmation of a treaty after it has been signed, which binds the state legally to the terms of the treaty.