Hemoglobin is a complex of which of the following?

The metal cation present in sodium nitroprusside is also present in:

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

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

What metal is present in Wilkinson's catalyst,which is used as a homogeneous catalyst for the hydrogenation of alkenes?