Goldenrod city, you battle Whitney and her evil mootank.
the third gym is in golden rod city
liquid crystal? do you mean Pokemon crystal if its Pokemon crystal the levels are 19 20 and 23
defeat Whitney the third gym leader
In the goldenrod gym.
At burned tower
Outside Cianwood City Gym.
Assuming you mean the hm fly on Pokemon crystal, you get it from the lady out side of Cindawood gym.
Talk to the woman outside the Cianwood City Gym.
just go to mauville city and you'll find the gym
In the mahogany gym
you capture the ledgon dariy Pokemon
In Pokémon HeartGold, you can find the 3rd Gym Leader in Goldenrod City.