Like (C), the physicist doesn’t rely on the idea that it’s impossible to know either the position or velocity of all subatomic particles. The physicist’s point is just that we can’t know both of those things at the same time.

This gets the argument backwards. The physicist claims that the states of particles are unknowable to imply that the complete state of the universe is unknowable—which is totally reasonable.

Like (A), this isn’t a flaw because it isn’t an assumption the physicist actually makes. The physicist’s point is that we can’t ever know both of these things at the same time. Whether we can know one or the other is irrelevant.

This is the flaw, because the physicist only focus on our knowledge about the universe, but draws a conclusion about the factual state of the universe. Without a link between knowledge and the factual state of the universe, the conclusion isn’t supported.

This just isn’t the case—if no individual particle’s position and velocity can be measured at the same time, then of course the position and velocity of all particles can’t be measured at the same time.