Introduction:
The complex ion No(CO)4 can exist in two different configurations, square planar and tetrahedral. The magnetic moment of a complex ion is a measure of the magnetic field that the ion exhibits. It is influenced by the arrangement of the electron spins in the complex ion. In this response, we will discuss the magnetic moment of the No(CO)4 complex ion in both square planar and tetrahedral configurations.

Square Planar Configuration:
In a square planar configuration, the No(CO)4 complex ion has a square planar geometry with four ligands arranged in a plane around the central No atom. The ligands, CO molecules, are strong-field ligands that form sigma bonds with the central No atom. The square planar geometry results in a d8 electron configuration for the No atom, where all the d orbitals are filled.

Magnetic Moment in Square Planar Configuration:
In a square planar configuration, the No(CO)4 complex ion has a magnetic moment of 0. This is because the d orbitals in the No atom are completely filled, resulting in paired electrons with opposite spins. The cancellation of the magnetic moments of the paired electrons leads to a net magnetic moment of 0 for the complex ion.

Tetrahedral Configuration:
In a tetrahedral configuration, the No(CO)4 complex ion has a tetrahedral geometry with four ligands arranged around the central No atom. The tetrahedral geometry results in a d9 electron configuration for the No atom, where one of the d orbitals is unpaired.

Magnetic Moment in Tetrahedral Configuration:
In a tetrahedral configuration, the No(CO)4 complex ion has a non-zero magnetic moment. This is because the d9 electron configuration results in one unpaired electron with a spin. The unpaired electron contributes to the magnetic moment of the complex ion, leading to a non-zero value.

Conclusion:
In conclusion, the magnetic moment of the No(CO)4 complex ion depends on its configuration. In a square planar configuration, the magnetic moment is 0 due to the complete filling of the d orbitals. In a tetrahedral configuration, the magnetic moment is non-zero due to the presence of an unpaired electron.