Final answer:
The electronic configuration (Ar4s0 3d2) indicates a +2 oxidation state for chromium. In combination with oxygen (with an oxidation number of -2), the chromium oxide formula is CrO, which is option a).
Step-by-step explanation:
The electronic configuration of chromium ion mentioned in the question is (Ar4s03d2). This implies that the chromium ion has lost two electrons, resulting in a +2 oxidation state for chromium. Based on this oxidation state and the fact that the oxidization number of oxygen is typically -2, the formula of the oxide would be CrO, with one chromium (Cr) ion bonding to one oxygen (O) atom.
The correct answer makes use of the electronic configuration given to determine the oxidation number and thus the chemical formula of the oxide. Hence, the correct formula of the oxide where chromium has an electronic configuration of (Ar4s03d2) is option a) CrO.