When acetic acid and $K_4[Fe(CN)_6]$ are added to a copper salt,a chocolate precipitate is obtained of the compound:

Which one of the following gives Prussian blue colour?

What metal is present in Wilkinson's catalyst,which is used as a homogeneous catalyst for the hydrogenation of alkenes?

The compound used in the treatment of lead poisoning is

Identify $(A)$ to $(E)$ and also explain the reactions involved.
$CuCO_3 \to CuO$ $\xrightarrow{\text{Heat with } CuS} (A)$ $\xrightarrow{\text{conc. } HNO_3} (B)$ $\xrightarrow{NH_{3(aq)}} (C) \text{ (Blue solution)}$
$CuCO_3 \to (D)$ $\xrightarrow{Ca(OH)_2} (E) \text{ (Milky)}$ $\xrightarrow{CO_2} Ca(HCO_3)_2 \text{ (Clear solution)}$

$A$ metal complex absorbed orange light. The colour in which it appears is