On cinnibar island.
the seventh gym is the first gym at the begining of the game. the leader is giovani of team rocket. he's ground and normal 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.
The 8th gym leader is in Viridian City.
In the mahogany gym
The seventh gym leader is Candice, the Ice Type leader. She is at Snowpoint City.
The key is in the Pokemon mansion.
You go on to defeat the eight gym leader.
Viridian City, Giovanni(Team Rocket Leader) is the Gym leader.
Step on the portals until you get to the gym leader.
In Fuchisa city
beat the gym leader
Her name is Erika