I'll try!
1) b is correct. Although Rain Repellent does put a film between the windscreen and the rain, it does (drastically!) aid the water to run off.
2)a. I don't know of any aircraft that is allowed to take off with de/anti ice selected on, although no doubt someone will come along and prove me wrong.
3) Depends on the a/c and SOP's, but I think you can generally say b is correct. Out aircraft is permitted to take off with frost on the underside of the wing, on the fuselage and nacelles, providing it is thin enough so detail can be made out beneath it. I.e. if you can still read the warning stickers, see rivets etc, you can go. But not with frost on the top of the wing.
4)Not sure, but would go with a.
Good Luck!