I think you are allowed to do more than one if you want but they'll only count your best one. I think. I could be very wrong on that. Regardless, you can't go above 100/100, these guys are trolls and you shouldn't have time to do more than one option imo
what my teacher told me for IPT (we had to do 2 options + core) is if you did all option topics, they would count only the first two or something you did (chronologically). I suppose it might be the same for physics dunno. ideally you wouldn't want to waste more time doing more than one option topic because they don't add all your option topics together to give you a score or average them, if you got like 8 out of the whole topic and in another topic you got 15 you wouldn't get the average of those two. But I think they don't give everyone marks for the best topic they did, I think they stick to the 'first option topic you answered chronologically irrespective of marks' criteria, so if you only do 1 option topic then you get your mark set for that.
but logically what you are taught at school, you should do that in the exam, I mean you wasted a whole term learning that option you might as well wrap your head around it and do it in the exam