Ramu is the elected leader / and also a person / who we all / can confide in.

Answer: Option C

The phrase "who we all can confide in" contains a grammatical error in the use of the relative pronoun.

Here, "who" is incorrectly used as the object of the verb "confide in." Since it functions as an object, the correct relative pronoun should be "whom".

So the correct sentence should be:
"Ramu is the elected leader and also a person whom we all can confide in."

"Whom" is used when referring to the object of a verb or preposition, whereas "who" is used as a subject.

Hence, the error lies in Option C.