Answer :
From the given balanced chemical reaction, it can be seen that each aluminum atom gains loses 3 electrons. Also, each copper atoms gains 2 electrons. The choice that would best give us the described scenario above is choice number 2. That is Each Al loses 3e- and each Cu gains 2e-.
The correct answer is option (2) i.e. Each Al loses 3e- and each Cu^2+ gains 2e-
When an atom X, loses an electron, it becomes, X^1+
When an atom X, loses two electrons, it becomes, X^2+
When an atom X, gains an electron, it becomes, X^1-
When an atom X, gains two electrons, it becomes, X^2-
So, Here, 2Al + 3Cu^2+ --> 2Al^3+ + 3Cu,
When each Al, loses three electrons, it becomes, Al^3+
When each Cu^2+, gains two electrons, it becomes, Cu^2+^2- = Cu
