paras at Ilex forest or a psyduck in random small bodies of water are some common ones.
i dont think nobody knows its in the bell sprout tower after you defeat the main guy
Yes.
Most electric type and psychic type pokemon can learn flash.
Oddish or Gloom.
yes. there is 7 in Pokemon crystal e.g: Strength, Flash, Fly, Surf, Whirlpool, Cut and Waterfall.
From the elder in the sprout-tower, after beating him of course.
how do you use flash? just go to pokemon and go to the pokemon that knows flash. press A and it will say in blue text "Flash" select that and it will use Flash. it's very useful in dark caves.
You find it at the Lake of Rage. You need a Pokemon that knows Surf to get to it.
Lugia because it knows water moves and ho oh dont and they are the ultimates of crystal.
bellsprouts can learn it or pikachu (EDIT)** my togepi knows it
Pokemon Crystal only contained seven HMs. The 8th HM Rock smash isn't available until later generation games. The HM one can get in Pokemon Crystal are cut, fly, whirlpool, waterfall, strength, flash, and surf.
I hate to be the bearer of bad news but you can not catch a Pokemon that already knows that as its an TM for soul~silver and a HM for the original silver.