If relative permeability of iron is 5500, then its susceptibility is 

Relation between relative permeability $\left({\text{μ}}_{\text{r}}\right)$ and susceptibility $\left({\text{χ}}_{\text{B}}\right)$ is

${\text{μ}}_{\text{i}}{\text{\hspace{0.17em}=\hspace{0.17em}1\hspace{0.17em}+\hspace{0.17em}χ}}_{\text{B}}$

$\Rightarrow {\text{\hspace{0.17em}\hspace{0.17em}χ}}_{\text{B}}{\text{\hspace{0.17em}=\hspace{0.17em}μ}}_{\text{r}}\text{-1}$

= 5500 – 1 = 5499