It is a <u><em>chemical compound</em></u> formed with a metal (mainly positive cations) with oxygen.
It is formed through the air as they react in the air together.
They are also BASES - ALKALINE (so neutralise acids)
Oxidation-Reduction Reactions Suggested Reading Thus the oxidation number for oxygen in calcium oxide is -2. ... In effect, each calcium atom loses two electrons to form Ca2+ ions, and each O atom in O2 gains two electrons to form O2- ions. The net result is a transfer of electrons from calcium to oxygen, so this reaction is an oxidation-reduction reaction.
+<u>O²</u><u>(</u><u>g</u><u>)</u><u>=</u><u>2</u><u>CaO</u><u>(</u><u>s</u><u>)</u>
Explanation:
we can conclude that in the reaction there is both reduction and oxidation.
Answer: metal
Explanation: it says element so conductor and semiconductor are out and a halogen is a group of gases on the periodic table so this brings up to a conclusion of metal.
NOTE: I am not a professional***