Chromium(II) oxide

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. Hypophosphites may reduce chromium(III) oxide to chromium(II) oxide:


 * H3PO2 + 2 Cr2O3 → 4 CrO + H3PO4

It is readily oxidized by the atmosphere. CrO is basic, while CrO3 is acidic, and Cr2O3 is amphoteric.

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.