<p>Well I don’t think UCSD cares about what type of SAT IIs you take, because I applied for Computer Engineering with a 740 on the Chem SAT II, with no Physics SAT II (however, my highest SAT IIs were Chinese 800 and Math II 780).
If you are better at Chem, I wouldn’t see any reason not to retake, but truth is, you probably need to be good in Physics. :D</p>