1 molecule CO2 has 2 atoms O.
1 mole CO2 has 2 moles O,
1.5 mole CO2 has 2*1.5 mole O=3.0 mole O
The nucleus of a atom contains the protons and the neutrons all most all of the atoms mass is weigh by the protons and the neurons.
From own experience, I know that OsO4 is colorless, but Cr2O3 is actually a solid green from what I have seen. but I guess it could appear yellow-greenish.
I think the answer would be Ga3+