$A$ solution of $FeCl_3$ when treated with $K_4[Fe(CN)_6]$ gives a Prussian blue precipitate due to the formation of:

In a complexometric titration of a metal ion with a ligand,the reaction is $M$ $(Metal-ion)$ + $L$ $(Ligand)$ $\to$ $C$ $(Complex)$. The end point is estimated spectrophotometrically (through light absorption). If '$M$' and '$C$' do not absorb light and only '$L$' absorbs,then the titration plot between absorbed light $(A)$ versus the volume of ligand '$L$' $(V)$ would look like:

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$[Cr(NH_3)_6]^{3+} + 6HCl \longrightarrow Cr^{3+}(aq.) + 6NH_4Cl$

When potassium ferrocyanide crystals are heated with concentrated sulphuric acid,the gas evolved is

Hemoglobin is a complex of which ion?

Identify the complexes formed in the following processes:
$I$. Mond's process for purification of nickel
$II$. Removal of unreacted $AgBr$ from photographic plates
$III$. Removal of lead poisoning from the body