Explanation:

Correct answer is (b). The error in the second part of the sentence is that the proper noun, ‘United States of America' has to be referred as ‘the United States of America’. Therefore changing the sentence to ‘There are a number of Indians living in the United States of America who flee there to study but are now settled there.’ is more appropriate. This is because we use 'the' before a group of something. E.g. The box of chocolates, The talented students of class 9, The United states of America. etc. Generally we never put 'the' before a country like 'India, Bangladesh, Sri lanka etc.' but we put 'the' for countries having a group of states in its name.Thus the article is missing from the sentence and thus the error is in part b of the sentence.