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.
It is readily oxidized by the atmosphere. CrO is basic, while is acidic, and 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.
Hypophosphites such as hypophosphorous acid can reduce chromium(III) oxide to chromium(II) oxide: