Step 1: Checking Each Option:
(i) should be ‘by your watch’, not ‘in your watch’; (iii) should be ‘a useful book’, since ‘useful’ begins with a consonant sound (/j/), not ‘an useful’; (iv) is a debatable usage — in standard style, ‘noise’ as an uncountable disturbance does not usually take the article ‘a’.
Step 2: Final Answer:
(ii) ‘Ganga is a holy river.’ is grammatically correct and unambiguous.