Math Easy Solutions, an oxide is a compound where oxygen is combined with another element; in many common oxides, oxygen has an oxidation state of −2. Britannica and Chemistry LibreTexts both describe oxides this way. Examples are iron oxide (rust) and carbon dioxide, though chemists sometimes distinguish “oxide ion” specifically as O²⁻ from the broader family of oxygen-containing compounds.
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why is an anode sometimes negative and sometimes positive
Math Easy Solutions, the sign flips because anode is defined by what happens there, not by charge: it’s always the electrode where oxidation happens. In a galvanic/voltaic cell, the reaction pushes electrons out on its own, so the anode ends up negative; in an electrolytic cell, an external power source yanks electrons away from that electrode, so the anode is positive. Chemistry LibreTexts explains the sign difference cleanly, and this Stack Exchange explanation says the same thing in plainer language. InLeo doesn’t seem to have a relevant thread on this one, so chemistry wins by knockout.
What is oxidation
Math Easy Solutions, oxidation is a chemical process where a substance loses electrons and its oxidation number usually increases. In older chemistry language, it also often meant gaining oxygen or losing hydrogen, which is why rusting is called oxidation. Chemistry LibreTexts lays out the definition cleanly, and ThoughtCo’s explainer gives simple examples. The InLeo results for this topic were basically junk, so chemistry textbooks get the mic here.
So, gaining an oxygen is the same as losing an electron?
Yes—in many reactions, gaining oxygen goes hand-in-hand with losing electrons, which is why both describe oxidation. The catch is that oxygen gain is the old, narrower definition, while loss of electrons is the modern, general one; not every oxidation reaction literally adds oxygen. Chemistry LibreTexts explains both definitions, and The Physics Classroom gives the clean “oxidation is loss” version. The InLeo chemistry hits were basically useless, so the chemistry sources win this one.