In the question parts have been underlined. If any rule of correct English is violated then it could be only in the UNDERLINED part, marked as 1, 2, 3 or 4. Choose the option, which violates usage of correct English Ganesh is taller than/1 Ramesh but/2 Anoop is/3 more taller/4.
To identify the incorrect usage in the sentence, let's examine each underlined part:
Taller than/1: This is a correct comparative form, as "taller than" is used to compare two entities, Ganesh and Ramesh.
But/2: The conjunction "but" is appropriately used here to contrast two different comparisons.
Is/3: The verb "is" is good to use after the subject Anoop, indicating a state of being.
More taller/4: This is incorrect as "taller" is already a comparative adjective, and using "more" is redundant. The correct phrase should be simply "taller."
Thus, the part that violates the correct usage of English grammar is only 4.