Magnetic susceptibility is a measure of how a substance responds to an external magnetic field. In the case of benzene, it is a diamagnetic molecule, meaning it has no unpaired electrons and will be slightly repelled by a magnetic field.To calculate the magnetic susceptibility of benzene, we can use quantum chemistry calculations. One common method is to use the Pascal's relations, which relate the magnetic susceptibility to the molecular orbital MO energies and occupations. For benzene, the MO diagram consists of three doubly degenerate orbitals E1, E2, and E3 and their corresponding antibonding orbitals E1*, E2*, and E3* . The occupied orbitals are E1, E2, and E3, while E1*, E2*, and E3* are unoccupied.Using Pascal's relations, the magnetic susceptibility of benzene can be calculated as: = -1/3 * n1 * E1* - E1 + n2 * E2* - E2 + n3 * E3* - E3 where n1, n2, and n3 are the occupation numbers of the orbitals E1, E2, and E3, respectively. In the case of benzene, n1 = n2 = n3 = 2.Upon the addition of a nickel atom to the benzene molecule, the magnetic properties will change due to the interaction between the unpaired electrons in the nickel atom and the electrons in the benzene ring. Nickel has two unpaired electrons in its 3d orbitals, which can interact with the orbitals of benzene, leading to the formation of new molecular orbitals and a change in the magnetic susceptibility.To calculate the new magnetic susceptibility, we would need to perform quantum chemistry calculations, such as density functional theory DFT or ab initio calculations, to obtain the new molecular orbital energies and occupations for the nickel-benzene complex. Then, we can use the same Pascal's relations to calculate the magnetic susceptibility of the complex.The observed changes in magnetic properties upon the addition of a nickel atom to the benzene molecule can be attributed to the interaction between the unpaired electrons in the nickel atom and the electrons in the benzene ring. This interaction can lead to the formation of new molecular orbitals with different energies and occupations, which in turn can affect the magnetic susceptibility of the complex.