CPV code 24212100 designates Chromium oxide in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
24212100 is a leaf code — the most specific level of its branch — so it can be used directly as the main CPV code of a contract notice. If it does not quite fit, check the neighbouring codes under 24212000 (Chromium, manganese, magnesium, lead and copper oxides and hydroxides).