Potassium manganate `(K_2MnO_4)` is formed when
A. chlorine is passed into aqueous `KMnO_(4)` solution
B. manganese dioxide is fused with KOH in air
C. formaldehyde reacts with potassium permanganate in the presence of strong alkali
D. potassium permanganate reaction with conc. `H_(2)SO_(4)`