Chromium(II) oxide (CrO) is an inorganic compound composed of chromium and oxygen. It is a black powder that crystallises in the rock salt structure.Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier
Properties It is readily oxidized by the atmosphere. CrO is basic, while is acidic, and is amphoteric.Chemistry 7th edition, by Raymond Chang page 645 (problem 15.100)
Occurrence CrO occurs in the spectra of luminous red novae, which occur when two stars collide. It is not known why red novae are the only objects that feature this molecule; one possible explanation is an as-yet-unknown nucleosynthesis process.
Preparation Hypophosphites such as hypophosphorous acid can reduce chromium(III) oxide to chromium(II) oxide:
H3PO2 + 2 Cr2O3 → 4 CrO + H3PO4
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