Which of the following is a chocolate brown complex?

If a didentate ligand ethane-$1, 2$-diamine is progressively added in the molar ratio $en : Ni :: 1: 1, 2: 1, 3: 1$ to $[Ni(H_2O)_6]^{2+}$ aqueous solution,the following coordination entities are formed:
$I$. $[Ni(H_2O)_4en]^{2+}_{(aq)} -$ pale blue
$II$. $[Ni(H_2O)_2(en)_2]^{2+}_{(aq)} -$ blue/purple
$III$. $[Ni(en)_3]^{2+}_{(aq)} -$ violet
The wavelengths in $nm$ of light absorbed in the case of $I$ and $III$ are respectively:

Which of the following is considered as an anticancer species?

$Fe^{3+}$ cation gives a Prussian blue precipitate on addition of potassium ferrocyanide solution due to the formation of:

Dimethyl glyoxime gives a red precipitate with $Ni^{2+}$,which is used for its detection. To get this precipitate readily,the best $pH$ range is

Match List-$I$ with List-$II$.

List-$I$	List-$II$
$(a)$ Chlorophyll	$(i)$ Ruthenium
$(b)$ Vitamin-$B_{12}$	$(ii)$ Platinum
$(c)$ Anticancer drug	$(iii)$ Cobalt
$(d)$ Grubbs catalyst	$(iv)$ Magnesium

Choose the most appropriate answer from the options given below: