What is the basic principle of the magnetic compass?

Correct Answer: Option C — Magnetic materials of the same polarity repel each other and those of opposite polarity attract.

The fundamental principle of the magnetic compass relies on the law of magnetism: like poles repel, and opposite poles attract. The compass needle, being a magnet, aligns itself with the Earth's magnetic field because the north-seeking pole of the needle is attracted to the Earth's magnetic south pole.