The addition of dilute \( \mathrm{NaOH} \) to \( \mathrm{Cr^{3+}} \) salt solution will give :
precipitate of \( \mathrm{Cr(OH)_3} \)
a solution of \( [\mathrm{Cr(OH)_4}]^{-} \)
precipitate of \( \mathrm{Cr_2O_3(H_2O)_n} \)
precipitate of \( [\mathrm{Cr(OH)_6}]^{3-} \)
