Which complex absorbs the wavelength of red light?

Which of the following exhibits highest molar conductivity?

Aqueous copper sulphate solution (blue in colour) gives:
$(i)$ a green precipitate with aqueous potassium fluoride,and
$(ii)$ a bright green solution with aqueous potassium chloride
Explain these experimental results.

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.

The hydrated $Cu^{2+}$ ion is:

The formula of the complex formed in the ring test for $NO_2^-$ and $NO_3^-$ is .....