In aqueous solution meta-aluminate ion exists as

• Meta aluminate ions are present in aqueous solutions as isolated aluminate ions are ${\mathrm{AlO}}_2^{-}$.Four water molecules surround it in solution, and two of them interact with the oxygen to produce the final product $4{\mathrm{OH}}^{-}$ groups. Coordinate bonds hold the four hydroxyl groups and two water molecules together in the complex.

Hence, the formula is ${\left[\mathrm{Al}(\mathrm{OH}{)}_4{\left({\mathrm{H}}_2\mathrm{O}\right)}_2\right]}^{-}$