The magnetic lines of force due to a bar magnet are:
(a) Curved lines    (b) Radially outward        (c) Concentric circles    ;(d) Parallel and straight

The correct answer is option (a) Curved lines.

The magnetic lines of force due to a bar magnet are Curved lines.

In the case of a bar magnet, the magnetic field lines always begin (or leave) from the N-pole of a magnet and end (or enter) at the S-pole of the magnet. They are curved lines.