The magnetic field lines outside the bar magnet:

A magnetic field line is an imaginary line such that a tangent to it at any point gives the direction of the magnetic field at that point in space.

Magnetic field lines are drawn to represent the magnetic fields.

Magnetic field lines can be drawn with the help of a magnetic compass.

Magnetic field lines are also called magnetic lines of force.

Properties of magnetic field lines:

1. The magnetic field lines of a magnet (or a solenoid) form continuous closed loops.

2. The magnetic field lines start from the north pole and end on a south pole outside the magnet. Inside the magnet, the magnetic field lines start from the south pole and end on the north pole.

3. The tangent to the magnetic field line at a given point represents the direction of the net magnetic field B at that point.

4. The larger the number of field lines crossing per unit area, the stronger is the magnitude of the magnetic field B.

5. The magnetic field lines do not intersect with each other if they did, there will be two directions of the magnetic field at that point which is not possible.

The magnetic field lines start from the north pole and end on a south pole outside the magnet. Hence, option B is correct.

Inside the magnet, the magnetic field lines start from the south pole and end on the north pole.