Zapdos will learn Thunder on it's on sometime around level 60.
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A typlosion can learn explsion
In LeafGreen Pikachu learns Thunder at level 41.
it learns peck, agility, thunder,thunder bolt,shock wave,sky attack,drill peck, fly,arial ace steel wing,wing attack
All Pokemon with a water-type can learn it. There are some other Pokemon that can learn it, but mostly water-Pokemon.
It can't learn that move cause it doesn't exist in leafgreen.