I think the answer is 2Mg + H2O4 = Cu12O4 + 2H
I’m really not sure though so it might be wrong… I’m not the best at balancing equations lol
You may tell when a solution os formed when the item or particle, such as sugar or salt,
dissolves completely in the solvent, such as water.
Basically, you know when a solution is formed when the material you have placed in the solvent disappears :P
Answer: these are just options, what is the main question, without it, we cannot determine which option is correct, so please repost the question.
Answer: The correct option is 3.
Explanation: We are given a compound which is made up of iron and oxygen only. The ratio of the two are given as:

This means that, number of iron ions are 2
Number of oxide ions are 3
From the above information, the formula becomes : 
The valency of iron = 3
Valency of oxide = 2
This compound is named as iron (III) oxide.
Hence, the correct option is 3