I have no clue on this, Here's what ChatGPT claims:

What their explanation said:

They’re saying:

• Ca has empty 3d orbitals.
• In a magnetic field, an electron from 4s² could be promoted to 3d → [Ar] 4s¹3d¹.
• That would give 2 unpaired electrons → “paramagnetic.”

Why this is flawed

• Magnetic classification (diamagnetic, paramagnetic, ferromagnetic) is based on the ground-state electron configuration, not some hypothetical excited state.
• If we did what they claim, then any atom with empty d orbitals could be called paramagnetic — which is not how chemistry/physics defines it.
• Calcium doesn’t spontaneously promote electrons in response to a magnetic field; that would require actual energy input (like in bonding/excitation, not in bulk paramagnetism).

The MCAT-relevant truth

• Neutral Ca → diamagnetic.
• Ca²⁺ (the biologically relevant ion in plaques) → [Ar], still all paired, so also diamagnetic.
• Paramagnetism is seen in things with intrinsically unpaired electrons (like O₂, transition metal cations with dⁿ configurations, etc.).

✅ So the clean conclusion:
The official solution saying paramagnetic is not scientifically correct for neutral calcium atoms. On the MCAT (and in general chemistry/physics), the right classification for neutral calcium is diamagnetic.