Which of the following compounds contains ionic,covalent,and coordinate covalent bonds?

The mismatched combinations are
$A.$ Chlorophyll $- Co$
$B.$ Water hardness $- EDTA$
$C.$ Photography $- [Ag(CN)_2]^-$
$D.$ Wilkinson catalyst $- [(Ph_3P)_3RhCl]$
$E.$ Chelating ligand $- D^{-}$\text{Penicillamine}
Choose the correct answer from the options given below:

Write the application of coordination compounds in black and white photography.

Prussian blue is formed when

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:

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