In which of the following complex ions is the central metal atom's $d$-orbital devoid of electrons?

Which of the following is true for the complex $[Fe(CN)_6]^{4-}$?

$A$ complex involving $dsp^2$ hybridization has:

An aqueous solution of $NiCl_{2}$ was heated with excess sodium cyanide in the presence of a strong oxidizing agent to form $[Ni(CN)_{6}]^{2-}$. The total change in the number of unpaired electrons on the metal centre is $.....$

Which of the following statements is not correct?

In a square planar complex of $Co^{2+}$ ion,the unpaired electron is present in which orbital?