Zinc dissolves in excess of aqueous alkali. Zn+2OH−+2H2O⟶[Zn(OH)4]2−+H2↑( Tetrahydroxozincate(II) ion) However, this reaction in NCERT is given as Zn+2NaOH⟶Na2ZnO2+H2↑ ZnO22− is anhydrous form of [Zn(OH)4]2−. ZnO22−+2H2O⇌[Zn(OH)4]2− So in aqueous medium best answer of this question is [Zn(OH)4]2−.