Correct Answer - Option 1 : The gemstone, ruby, has Cr3+
ions occupying the octahedral sites of beryl.
The gemstone, ruby, has Cr3+ ions occupying the octahedral sites of Aluminium oxide (Al2O3) while beryl is beryllium aluminium cyclosilicate (Be3 Al2 Si6 O18) which is a variety of emerald and aquamarine.
[Ni(NH3)4 (H2O)2]2+ = Ni 2+ → 3d8 → 2 unpaired electron
Where, μm = 2.83 BM
The complimentary colour of violet is yellow.
A colour that combined with a given colour makes white or black is called complimentary colour.
[Fe(H2O)6]2+, Fe2+ → 3d6 → 4 unpaired electron
[Cr(H2O)6]2+, Cr2+ → 3d4 → 4 unpaired electron
Thus, the spin-only magnetic moments are nearly similar.
Among the given statements, the statement in option (a) is incorrect.