<span>physical changes
Physical changes happen when something undergoes a transformation that does not alter their total inward arrangement. This appears differently in relation to the idea of compound change in which the creation of a substance changes or at least one substances consolidate or separate to frame a new one</span>
D-sublevel can occupy 10 electrons whereas s-sublevel can occupy 2 electrons...
For [Ni(en)³]²⁺ which is purple, the crystal field splitting energy is greater than the complex ion, [Ni(H₂O)₆]²⁺ which is green in color.
When a Lewis base id attached to the metal ion by covalent bond, then the complex ion is formed and when these complex ions are present with other ions of opposite charge or neutral charge, they will make complex compounds.
I would say b and d but I wouldn’t really know :/