To a Concentrated Buffer of PH 4

Multiple Choice

To a concentrated buffer of pH 4.0 is added an equal volume of a solution that is 0.020 M in Cr3⁺, Cd²⁺ and Al³⁺. The expected precipitate would consist of ________.
salt: chromium(III) hydroxide   cadmium hydroxide   aluminum hydroxide
Ksp  6.3 × 10^-31            2.5 × 10^-14        1.3 × 10^-33

A) Al(OH) ₃
B) Al(OH) ₃ and Cr(OH) ₃
C) Cd(OH) ₂
D) Cd(OH) ₂ and Cr(OH) ₃
E) Cd(OH) ₂, Cr(OH) ₃ and Al(OH) ₃