(i) 2,2-dimethylpentane (because for the two alkyl groups on the same carbon, its locant is repeated twice)
(ii) 2, 4, 7-trimethyloctane (because 2, 4, 7-locant set is lower than 2, 5, 7).
(iii) 2-chloro-4-methylpentane. (Alphabetical order of substituents)
(iv) But-3-yn-l-ol (because lower locant for the principal functional group, i.e., alcohol).