Question

The ferricyanide complex ion is ____

Answer 1

The oxidation state of $Fe$ in $\left[Fe\right(CN{)}_6{]}^{3-}$ ion is +3, and configuration $3d^5$ thus $F{e}^{3+}$ have five unpaired electrons in 3d orbitals.
Cyanide ion is a strong field ligand forcing, two electrons to pair up leaving one unpaired electron in 3d. Six vacant orbitals form $d^{2}d{p}^3$ hybridised octahedral inner orbitals complex.
Because of the unpaired electron the complex is paramagnetic.
Hence option (a) is the correct answer.