The metal present in $Vitamin \ B_{12}$ is

When acetic acid and $K_4[Fe(CN)_6]$ are added to a copper salt solution,which substance forms a chocolate-brown precipitate?

Coordination compounds have significant importance in biological systems. In this context,which of the following statements is incorrect?

The compound used in the treatment of lead poisoning is

In the complex ion $[Co(CN)_6]^{3-}$,the $Co^{3+}$ ion absorbs radiation of the violet color from the visible spectrum. What will be the color of its aqueous solution?

Assign $A, B, C, D$ from the given type of reaction.
$K_4[Fe(CN)_6] + 2CuSO_4 \longrightarrow Cu_2[Fe(CN)_6] \downarrow + 2K_2SO_4$