A bar magnet has total length 2l = 20 units and the field point P is at a distance d = 10 units from the centre of the magnet

A bar magnet has total length 2l = 20 units and the field point P is at a distance d = 10 units from the centre of the magnet. If the relative uncertainty of length measurement is 1%, then uncertainty of the magnetic field at point P is

  (1) 10% 

(2) 4%

 (3) 3%

 (4) 5% 

                                                          (JEE-2025)