Answer
The formula unit of kanoite is $MgMn(SiO_{3})_{2}$.
Work Step by Step
2 $SiO_{3}^{2-}$ ions contribute a total of -4 charge. This negative charge is neutralized by 1 $Mg^{2+}$ ions and 1 $Mn^{2+}$ ions. Hence, formula unit of kanoite is $MgMn(SiO_{3})_{2}$.
