redox reaction 2(urgent)

1. 1. Which of the following solutions will give off colourless gases only during electrolysis using carbon electrodes?
A. Silver nitrate solution
B. Copper(II) sulphate solution
C. Sodium hydroxide solution
D. Concentrated sodium chloride solution
For option B, in anode, there are both OH^- and SO4^2- ions, since OH^- is a stronger reducing agent than SO4^2-, OH^- is preferentially discharged to give colourless oxygen gas. In cathode, there are both Cu^2+ and H+ ions, since Cu^2+ is a stronger reducing agent than H^+, Cu^2+ is preferentially dicharged, forming Cu deposited on cathode.
For option C, in anode, there are only OH^- ions, so OH^- discharged, giving oxygen gas. In cathode, there are both Na^+ and H^+ ions, since H^+ is a stronger oxidizing agent than Na^+, so H^+ is preferentially discharged, forming colourless hydrogen gas. So only colourless gases are formed in the electrolysis using NaOH as electrolyte.
i.e. To determine whether a substance is a stronger oxidizing/reducing agent, please refer to the E.C.S.

2. The O.N. of Mn in MnO4^- is so higher that it tends to 'lower' itself to a lower level by reduction. Hence it should be a strong oxidizing agent.

3. Guess: I think it is related to the size.

4. Obviously, the answer is B.