To identify the specific arrow on a diagram that represents the Senate's power to approve or reject presidential appointments, I would need to see the diagram in question. Typically, this would be an arrow pointing from the Senate to the Executive branch or directly to the president, indicating the Senate's role in confirming or rejecting appointments made by the president.
If you have a description of the diagram or any specific labels related to the arrows, I could help guide you in identifying the correct one!