The correct option is C (a)
Let’s examine the sentence: “Mr. Smith was accused for murder but the court found him not guilty and acquitted him.” In Standard English, “accused” is used with “of” and not “for” followed by the crime. Hence, the correct sentence would be, “Mr. Smith was accused of murder but the court found him not guilty and acquitted him.” As the error is in part a of the sentence, Option A is the correct answer.