The question asks which constitutional article gave Parliament the primary legislative basis to enact the Air (Prevention and Control of Pollution) Act, 1981. Checking each article against its actual constitutional function identifies the right one.
Because the Air Act was passed pursuant to state resolutions requesting a uniform central law on a subject otherwise within the State List, Article 252 is the specific enabling provision, not Article 253's treaty-implementation power, Article 233's judicial appointment provision, or an absence of any applicable article.
Therefore, the correct answer is Article 252.