The equivalent weight of Al in ${\mathrm{Al}}_2{\mathrm{O}}_3 \mathrm{is}$

Equivalent weight of Al $=\frac{\mathrm{Atomic} \mathrm{weight} \mathrm{of} \mathrm{Al}}{\mathrm{Valency} \mathrm{of} \mathrm{Al}}$

We know that the element Al belongs to group IIIA; due to this reason valency of Al is 3.

Therefore, equivalent weight of Al in ${\mathrm{Al}}_2{\mathrm{O}}_3=\frac{27}{3}=9$