Identify the part which contains an error, if any :
They are newcomers (A)/ to the city,(B)/ isn’t ? (C)/ No error (D)

Correct option is C

The error is in part C, where the question tag is incorrect. The sentence is:
"They are newcomers to the city, isn’t ?"
This is a statement with a positive verb ("They are"), so the question tag must be negative, and it must match the auxiliary verb "are".
Correct form:
"They are newcomers to the city, aren’t they?"
Grammar Rule:
· A question tag should always match the auxiliary (helping) verb used in the main sentence.
· If the main sentence is positive, the question tag is negative, and vice versa.
· Example:
· She is coming, isn’t she?
· They aren’t ready, are they?