The reagent used for the detection of $Ni^{2+}$ is $A$. $x$ moles of $A$ react with $Ni^{2+}$ to form a complex of $C$ color. $A$,$x$,and $C$ are respectively:

Sodium thiosulphate is used in photography for which of the following purposes?

Which ligand is used in the estimation of the hardness of water?

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

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

Which ligand is useful for the removal of the toxic effect of lead metal in the body during chelate therapy treatment?