What is the color of a cobalt chloride solution?

From the stability constant (hypothetical values) given below,predict which is the strongest ligand:

Which of the following factors tends to increase the stability of metal ion complexes?

Assertion : Low spin complexes have lesser number of unpaired electrons.
Reason : $[FeF_6]^{3-}$ is a low spin complex.

When pyridine is added to an aqueous solution of nickel sulfate followed by the addition of an aqueous solution of sodium nitrite,deep blue crystals of .......... are obtained.

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$HgI_2 \downarrow + 2KI \longrightarrow K_2[HgI_4]$