Q. Assertion : Magnetic lines of force form continuous closed loops
Reason : Magnetic poles always occur in pairs as north pole and south pole

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Solution:

Magnetic poles exist in pairs. It is not possible to isolate a north pole or a south pole Magnetic field lines start from the north pole and go to the south pole and return to the north pole. They form continuous closed loops unlike electric lines of force which do not as electric monopole, single charge does exist