Which one of the following is an inner orbital complex as well as diamagnetic in behaviour ?
(Atomic no. : Zn = 30, Cr = 24, Co = 27, Ni = 28)

To determine which complex is an inner orbital complex and diamagnetic, we need to analyze the electronic configuration of each complex. So, let's consider each option: option 1 involves [Zn (NH3)6]2+, option 2 involves [Cr (NH3)6]3+, option 3 involves [Co (NH3)6]3+, and option 4 involves [Ni (NH3)6]2+. Notice that an inner orbital complex has a d2sp3 hybridization, and it is diamagnetic if it has no unpaired electrons. Think of it this way: the electronic configuration of the metal ion in the complex determines whether it is an inner orbital complex and whether it is diamagnetic. In other words, the complex must have a d2sp3 hybridization and no unpaired electrons to be an inner orbital complex and diamagnetic. Therefore, the correct answer is the option that involves the complex that meets these conditions, which is option 3.