An aqueous solution `FeSO_(4).Al_(2)(SO_(4))_(3)` and chrome alum is heated with excess of `Na_(2)O_(2)` and fltered. The materials obtained are
A. a colourless filtrate and a green residue
B. a yellow filtrate and a green residue
C. a yellow filtrate and a brown residue
D. a green filtrate and a brown residue