That depends on which region you are playing in. Since you didn't specify which region I will just list them all. If you are in Kanto then use psychic or ground type Pokemon as this is a poison type gym. If you are in Johto then use psychic or flying type Pokemon as this is a fighting type gym. If you are in Hoenn then use fighting type Pokemon or your strongest Pokemon as this is a normal type gym but the Pokemon have high hp and can be quite annoying. And finally, if you are in Sinnoh then use dark or ghost type Pokemon as this is a ghost type gym. Hope this helps.
Since the 5th gym leader is ground type, water or grass type are prefered.
The 5th gym leader has the following pokemon
Krokorok- lvl 29
Palpitoad- Lvl 29
Excadrill- Lvl 31
This means that these pokemon are different type along with ground and have different weaknesses.
Spinda then vigoroth then linoone then slaking
The fifth GYM is Fantina, she uses ghost pokemon. Ghost types are weak against: dark and ghost type moves.
Fantina is the 5th gym Leader in Hearthome the Ghost type gym.
electric type Pokemon
Veilstone city,the gym leader is a fighting type
fighting{I recommend alaczam and vespiquen}
there is no ninth gym. after the eight gym is the Pokemon league.
The Fifth Gym in Pokémon Pearl is the Ghost Gym so use Dark-type moves.
Fantina is the 5th gym Leader in Hearthome the Ghost type gym.
In Pokemon Pearl, the fifth gym is in Hearthome City. The gym leader, Fantina, uses Ghost type Pokemon. She will only be available to battle after the player gives the Old Charm to the elder in Celestic Town.
it is in hearthome city
The third gym leader in poekmon pearl is maylene, a fighting type gym leader.
electric type Pokemon
back to her gym
a fire type pokemon or a ground type
water
gardenia - grass type
what do you do after beating the fouth gym in pokemon pearl
Veilstone city,the gym leader is a fighting type