Question

If you are told that one of them is Cr2O3 and the other is OsO4, which one do you expect to be the yellow solid?

Cr2O3
OsO4

Answer 1

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.

Answer 2

Answer is: OsO₄ (osmium tetroxide or osmium(VIII) oxide).

Osmium(VIII) is colourless, but most samples appear yellow, because of the presence of the impurity OsO₂ (osmium(IV) oxide), which is yellow-brown in colour.

Cr₂O₃ (chromium(III) oxide) is light to dark green compound. It is used as a pigment. In this chemical compound chromium has oxidation number +3.