Final answer:
The sentence 'The economic priorities of democratic states are very different from autocratic states.' has a faulty parallel structure because the second noun phrase in the comparison is not fully stated.
Step-by-step explanation:
The sentence that best describes the faulty parallel structure in 'The economic priorities of democratic states are very different from autocratic states.' is 'The second noun phrase in the comparison is not stated completely.' In this sentence, the first element of the comparison refers to 'the economic priorities of democratic states,' but the second element should similarly relate to the economic priorities of autocratic states to maintain parallelism. To correct the faulty parallel structure, the sentence could be rephrased to 'The economic priorities of democratic states are very different from those of autocratic states.'