Final answer:
The correct answer is a) Mesiolingual cusp, which is the cusp located on the mesial lingual surface of the permanent maxillary first molar.
Step-by-step explanation:
The cusp on the mesial lingual surface of the permanent maxillary first molar is the Mesiolingual cusp. The maxillary molars have specific cusp naming that corresponds to their position in the mouth. The mesio part of the name indicates that the cusp is located towards the front of the mouth, while lingual signifies that it is towards the tongue. Therefore, the correct answer to the student's question is option a) Mesiolingual cusp.