In the trivalent state, most of the compounds are covalent and are hydrolyzed in water. Trichlorides, upon hydrolysis in water, form tetrahedral \([\text{M(OH)}_4]^-\) species, and the hybridization state of element M is \( sp^3 \).
In the case of aluminum, acidified aqueous solution forms octahedral \([\text{Al(H}_2\text{O)}_6]^{3+}\) ion.