What quality would an interactive proof executed many times sequentially have that makes it zero knowledge that one executed in parallel would not?
Hint: look at the security proof of the zero-knowledge property of the first scheme. I recommend writing it fully and formally, if you want the solution to become clear. It relies on a common "rewinding" strategy, and requires in particular to guess in advance the challenge of the verifier, with non-negligible probability. Now, what happens to this strategy when we consider parallel repetitions instead? Can you see where exactly it breaks down? We can give you further hints if you explain exactly what you tried and tell us where you are stuck afterward.