The correct option is B (b)
Let’s examine the sentence: “(a) Please (b) tell to him (c) to do his work.” The sentence uses the transitive verb “tell.” A transitive verb requires an object to complete its sense. Hence, the verb “tell” would be followed by the object “him” and not the preposition “to.” So, the preposition “to” should not exist between “tell” and “him.” Hence, the error is in Part B of the sentence. So, Option B is the correct answer.