Multiple choice general knowledge science & technology Fill in the missing word: _______ + oxygen = Magnesium oxide Magnesium Iron Manganese Metal Reveal answer Fill a bubble to check yourself A Correct answer Explanation Magnesium reacts with oxygen to form magnesium oxide (MgO) in a combination reaction. This is a classic example of a metal combining with oxygen. Iron would form iron oxide (rust), and the generic term 'metal' is too vague.