An element M reacts with another element X to form . In terms of loss or gain of electron, identify the element oxidized and reduced. I need help in understanding this question, I know what a redox reaction is in terms of loss or gain of electron. However, I am not able to solve this question. I think that's maybe because the oxidation state or valency is not given for the unknown elements. Like, how do I know if the element is gaining or loosing electron when I don't know it's valency.

I repeat, I need to UNDERSTAND this question, I already know the answer but am just confused about how to solve it...