In the complex ions \([Fe(C_2O_4)_3]^{3-}\). The coordination number of Fe is:

6

The correct answer is 1. 6

The coordination number of a metal ion in a complex is the number of ligands bonded to it. In the complex ion \([Fe(C_2O_4)_3]^{3-}\), the central metal ion is iron (Fe), and it is surrounded by three oxalate (\(C_2O_4^{2-}\)) ligands.

Each oxalate ligand can form two bonds with the metal ion (through the oxygen atoms), so the coordination number is determined by the number of these bonds. In this case, there are three oxalate ligands, and each forms two bonds.

Therefore, the coordination number of Fe in \([Fe(C_2O_4)_3]^{3-}\) is \(3 \times 2 = 6\).

So, the correct answer is 1. 6.