Which of the following complexes will exhibit maximum attraction to an applied magnetic field?

To determine which complex exhibits maximum attraction to an applied magnetic field, we need to look at the number of unpaired electrons in each complex. The more unpaired electrons a complex has, the greater the attraction to the magnetic field. <br/><br/> 1. Option A: [Ni(H₂O)₆]²⁺ Ni²⁺ has a 3d⁸ electron configuration. In an octahedral crystal field, two of the electrons will occupy the lower energy t₂g orbitals, while the remaining six electrons will fill the higher energy e_g orbitals. There are 2 unpaired electrons in this complex. <br/><br/> 2. Option B: [Co(H₂O)₆]²⁺ Co²⁺ has a 3d⁷ electron configuration. In an octahedral crystal field, two of the electrons will occupy the lower energy t₂g orbitals, while the remaining five electrons will fill the higher energy e_g orbitals. There are 3 unpaired electrons in this complex. <br/><br/> 3. Option C: [Co(en)₃]³⁺ Co³⁺ has a 3d⁶ electron configuration. In an octahedral crystal field, all six electrons will occupy the lower energy t₂g orbitals. There are no unpaired electrons in this complex. <br/><br/> 4. Option D: [Zn(H₂O)₆]²⁺ Zn²⁺ has a 3d¹⁰ electron configuration, with all orbitals being completely filled. There are no unpaired electrons in this complex. <br/><br/> Based on the number of unpaired electrons, the complex with the maximum attraction to an applied magnetic field is [Co(H₂O)₆]²⁺ (Option B), as it has 3 unpaired electrons.