Recollecting my mistake in CASTLE MathQ'2001

I jointly won the CASTLE MathQ'2001, a state-level mathematics competition held in late 2001, in which 900 candidates appeared. While I was happy that I scored the highest marks, even if jointly, I had a somewhat strong regret at that time (whose intensity, and perhaps importance, has faded with time).

I remember that on the test day, when the allotted time was just about to finish, I had reached at the last question of the question paper. I was probably at a back bench, so when the time-over alarm had sounded and the test administrator had started collecting the answer-sheets, I still had a few seconds left before my sheet was taken. I knew that I had moments left, and aggressive as I believe I generally am, it was my intent to extract even the last possible drops of marks from this competition, in order to maximize my position. I was in battle-fighting mode that day, I remember clearly.

My brain wasn't working as well at that moment as it had been working all through the test, and I concluded that in the few seconds left, I wouldn't be able to solve the last question to reach at an indisputable answer. What to do? Guesstimate? Or just leave? 1 mark for a correct answer, a negative 0.25 for an incorrect answer, and no marks for a blank.

Last page of my actual MathQ'2001 question paper

My winning certificate :)

Not sure why, but right before my answer-sheet was taken, I just marked the most-likely-looking option as the answer.

And it turned out to be incorrect. I lost an extra 0.25 mark that I wouldn't otherwise have lost. A narrow win became a joint-win. The first prize - a Vintron Biz123 desktop computer - changed into a joint prize. And I regretted this a lot (at that time at least).