Final answer:
The correct answer is option C) Ten days after the death of X, I promise to pay to the order of Y P10,000. Sgd. Z.
Step-by-step explanation:
Option C is not negotiable because the payment is dependent on the death of X. The death of X is not a determinable future time as it is unpredictable. Therefore, it does not meet the requirement of being payable at a determinable future time.
In contrast, options A, B, and D specify a specific future time when payment is due. Option A states that payment will be made one week after X passes the CPA Board Exam, option B states that payment will be made thirty days after demand, and option D states that payment will be made on or before October 31, 1998.
To summarize, option C is not negotiable because it does not meet the requirement of being payable at a determinable future time, as it depends on the unpredictable event of the death of X.