Identify the use of $EDTA$ from the following.

Acidic ferric chloride solution on treatment with excess of potassium ferrocyanide gives a Prussian blue coloured colloidal species. It is :

Which of the following is considered as an anticancer species?

Assertion: $AgCl$ dissolves in $NH_4OH$ solution.
Reason: Due to formation of a complex.

Aqueous solution of a metallic nitrate $X$ reacts with $NH_4OH$ to form $Y$,which dissolves in excess $NH_4OH$. The resulting complex is reduced by acetaldehyde to deposit the metal. $X$ and $Y$,respectively,are

$A$ reagent which gives a brilliant red precipitate with $Ni^{2+}$ ions in a basic medium is