Assertion (A) : The earth's magnetic field is due to iron present in its core. 

Reason(R) : At low temperature, magnet loses its magnetic property or magnetism.

Both A and R is false

The correct answer is option 3: Both A and R is false

Assertion (A): The earth's magnetic field is due to iron present in its core. This statement is false. The Earth’s magnetic field is not simply due to the presence of iron in the core. It is mainly produced by the motion of molten iron and nickel in the outer core, which creates electric currents and generates the magnetic field.

Reason (R): At low temperature, magnet loses its magnetic property or magnetism. This statement is also false. Magnets generally lose their magnetic properties at high temperatures (above the Curie temperature), not at low temperatures.

Therefore, both Assertion and Reason are false.