Hop in the elevator at the base of Prism Tower, in the heart of Lumiose City. The elevator will shuttle you up to the gym, where the gym leader's little sister is waiting. Each of the elevators behind her is guarded by a trainer, though only elevator leads to the next floor of the tower. You have to answer her questions by choosing the correctly-numbered elevator to proceed. You can guess as many times as you want if you'd like to fight all of the trainers. These fights are all rather simple, as you only take on one Pokémon at a time. Your primary concern is paralysis, since it's an Electric-type gym, though if you grabbed a Ground-type from Route 13 you should breeze through most of these battles.
All of the trainers you'll face are listed below. If you want to whiz through this gym you should only approach the 'Correct' elevators. Once you leave a floor you'll no longer be able to fight any remaining trainers, so don't approach the 'Correct' elevator until you've had your fill of battles.
First question
1. Schoolboy Arno (Incorrect)
2. Schoolboy Sherlock (Incorrect)
3. Schoolboy Finnian (Correct)
- Pachirisu, level 34
2. Schoolboy Sherlock (Incorrect)
- Stunfisk, level 34
3. Schoolboy Finnian (Correct)
- Dedenne, level 34
1. Rising Star Estel (Correct)
- Raichu, level 35
2. Rising Star Nelly (Incorrect)
- Magneton, level 35
3. Rising Star Helen (Incorrect)
- Manectric, level 35
1. Ace Trainer Mathis (Incorrect)
- Lanturn, level 36
2. Ace Trainer Mathis (Incorrect)
- Electrode, level 36
3.) Ace Trainer Rico (Correct)
- Ampharos, level 36
1. Poke Fan Abigail (Incorrect)
- Minun, level 34
2. Poké Fan Lydie (Correct)
- Plusle, level 34
3. Poke Fan Tara (Incorrect)
- Pikachu, level 34
Aaaaand that's that for the quizzes. On the next level you'll come to the Gym Leader.
Leader Clemont
- Emolga, level 35
- Magneton, level 35
- Heliolisk, level 37
Clemont is a bit painful, but not horrible even if you don't have Ground-type moves to rely on. Emolga is primarily annoying because it can inflict paralysis with Static, like so many things in this gym, and can't be hit with Ground-type attacks. Magneton is worse because of its durability, but also because it can electrify the battlefield and power up its moves. Fire is the preferred attack, though Ground works since this Magneton doesn't have Levitate. Just bear in mind that it has Sturdy, so you won't get a OHKO. Heliolisk is a bit of a surprise since it has Grass Knot to wipe out your Ground- or Rock-types, though it doesn't have much HP and can be trounced with a Ground- or Fighting-type move.
Beating Clemont will earn you the Voltage Badge, allowing you to control Pokémon up to level 70. You'll also receive TM 24 Thunderbolt.
Immediately after completing the gym and leaving you'll get a call from Sycamore. Head to the Lysandre Café in Magenta Plaza. After watching the cutscene that follows you'll receive a King's Rock. This is a handy evolutionary item for a few Pokémon. With that you'll be headed off to Route 14, leaving Lumiose City behind for a while.