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CrO, or chromium(II) oxide, is a binary oxide of chromium in the +2 oxidation state. It is one of the less common and less stable chromium oxides, with Cr2O3 and CrO3 being far more familiar. In air, CrO is readily oxidized to Cr2O3, reflecting the tendency of Cr(II) to convert to Cr(III) under oxidative conditions. Consequently, CrO is typically prepared and observed under strongly reducing conditions and is often encountered as a transient species, in gas-phase studies, or as a thin-film material.

In terms of structure and properties, CrO is described as a black or gray solid that is insoluble in water. The precise crystal structure of CrO is not as well established as those of more common oxides, but it is frequently treated as adopting a rock-salt-like monoxide lattice, with chromium in a divalent state coordinated to oxide. The compound is expected to be reactive toward oxidation and can exhibit paramagnetic behavior associated with Cr(II). Its stability is highly sensitive to temperature and the surrounding oxygen partial pressure.

Preparation and occurrence of CrO are typically limited to specialized contexts. It can be generated by reducing CrO3 or Cr2O3 under highly reducing conditions, such as high temperature in a hydrogen or inert environment, and can appear as a transient phase or as part of thin-film research. Due to its instability in air, CrO is mainly of interest in fundamental studies of chromium chemistry and oxide phases rather than practical applications.

Safety considerations reflect the broader hazards of chromium compounds. Cr(II) species can be toxic and are subject to hazards associated with inhalation or skin exposure; appropriate handling and disposal procedures should be followed.