Which of the following complex ions does not absorb visible light?

The correct increasing order of spin-only magnetic moment values of the complex ions $[MnBr_{4}]^{2-}$ $(A)$, $[Cu(H_{2}O)_{6}]^{2+}$ $(B)$, $[Ni(CN)_{4}]^{2-}$ $(C)$ and $[Ni(H_{2}O)_{6}]^{2+}$ $(D)$ is:

The number of geometrical isomers of a planar complex $M_{abcd}$ is

Identify the homoleptic complex(es) that is/are low spin.
$(A) \ [Fe(CN)_5NO]^{2-}$
$(B) \ [CoF_6]^{3-}$
$(C) \ [Fe(CN)_6]^{4-}$
$(D) \ [Co(NH_3)_6]^{3+}$
$(E) \ [Cr(H_2O)_6]^{2+}$
Choose the correct answer from the options given below:

Which one has the highest paramagnetism?

The type of isomerism shown by the complex $[CoCl_2(en)_2]$ is