A domain in a ferromagnetic substance is in the form of a cube of length $1\mu m.$  If it contains  $8\times {10}^{10}$ atoms and each atomic dipole has a dipole moment of  $9\times {10}^{-24}A{m}^2,$ then the magnetization of the domain is ______  $\times {10}^{4}A.m^{-1}.$

$$\begin{gathered} Volumeofcube\left(domain\right)={\left({10}^{-6}\right)}^3={10}^{-18}{m}^3 \\ Numberofatoms\left(N\right)=8\times {10}^{10} \end{gathered}$$

$Dipolemoment\left(M\right)=9\times {10}^{-24}A{m}^2$ for each atom
The maximum possible dipole moment $M_{\max }$ is obtained for case when all atomic moment at perfectly aligned. 
 Hence, $M_{\max }=NM=8\times {10}^{10}\times 9\times {10}^{-24}=72\times {10}^{-14}A{m}^2$
$\therefore Magnetization=\frac{M_{\max }}{Volume}=\frac{72\times {10}^{-14}}{{10}^{-18}}=72\times {10}^{4}A/m$