Define magnetic field. $A$ compass needle gets deflected when brought near a bar magnet. Why? List three properties of magnetic field lines.

(N/A) Magnetic field is the region around a magnet where its magnetic force can be experienced.
$A$ compass needle gets deflected because the magnetic field of the bar magnet exerts a force on the poles of the compass needle.
Properties of magnetic field lines:
$(i)$ The magnetic field lines emerge from the north pole and merge at the south pole outside the magnet.
$(ii)$ They are closed continuous curves.
$(iii)$ No two magnetic field lines intersect each other.