The fifth gym leader Koga uses Poison type pokemon so your best bet is to use Psychic or Ground types against them. A Kadabra(Alakazam would be even better) can easily take care of all of Koga's pokemon.
The fifth Gym can be found in Fuchsia City. The leader is Koga, who specialises with Poison-type Pokémon.
You go to Canalave City left of Jublife City. The gym leader there uses steel types. So be ready with fighting or water type Pokemon
The fourth gym at Pokemon fire red is grass type gym
In Pokemon Red, the fifth badge is possessed by the Poison-Type Koga. The badge is named Soul Badge. It lets you use Surf outside of Battle.
The fifth gym in Pokemon white uses the ground type.
To defeat Clay you must use water type Pokemon, cause he uses ground type.
The fifth Gym Leader in Pokemon LeafGreen is Koga, the leader of Fuschia City's Gym. He specializes in Poison-type Pokemon and hands out the Soul Badge.
Poison type pokemon, other trainers in the gym also have psychic but again the leader has poison type
with fighting type pokemon
It depends on the version. In Pokemon Ruby, Sapphire, and Emerald, the fifth gym leader is Norman. He specializes in using normal type Pokemon and he is your father. His Pokemon are 2 Vigoroth and 1 Slacking.
Clay, the fifth Gym Leader, uses Ground-Type Pokemon, so Water-Type Moves are good against it. One of his Pokemon is Palpitoad, which is a Water- and Ground-Type Pokemon, so it's probably best not to use Fire-Type Pokemon against this one. The other two Pokemon are Krokorok and Excadrill. Hope this helps.
He is your father back in petalburg city, take fighting types because he has normal type pokemon
go to the faris wheel
The fifth gym leader Koga uses Poison type pokemon so your best bet is to use Psychic or Ground types against them. A Kadabra(Alakazam would be even better) can easily take care of all of Koga's pokemon.
Chili (former gym leader)
its a normal type gym leader named lenora, gives out basic badge