$A$ magnetic intensity of $500 \,A/m$ produces a magnetic flux of $2.4 \times 10^{-5} \,Wb$ in an iron bar of cross-sectional area $0.4 \,cm^2$. The magnetic permeability of the iron bar is

• A
  $2.4 \times 10^{-3} \,T \cdot m/A$
• B
  $1.2 \times 10^{-3} \,T \cdot m/A$
• C
  $2.4 \times 10^{-4} \,T \cdot m/A$
• D
  $1.2 \times 10^{-4} \,T \cdot m/A$