The free space inside a current carrying toroid is filled with a material of susceptibility 2 × 10 - 2 …

It is given that 

${\chi }_m=2\times {10}^{-2}$

The permeability is ${\mu }_r=1+{\chi }_m=1+0.02=1.02$.

The magnetic field is $B={\mu }_r{B}_0=1.02B_0$

Hence, percentage increase in magnetic field is 

$\frac{B-B_0}{B_0}\times 100\%=\frac{{\displaystyle {{\displaystyle B}}_0}\left(1.02-1\right)}{B_0}\times 100\%=2\%$