You need the Mauville badge, go to Mauville and fight the gym leader, but you must first fight Wally to get to the door open.
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The 7th badge.
rock smash is hm06 and is found in mauville city but you need the dynamo badge to use it outside of battle
The fourth one.
you need the Mauville city gym badge. (the electricity gym) if im not mistaken
you need the HM rock smash and you need the required gym badge the see if any Pokemon you have can learn it if not go and find a Pokemon the can i would advise a fighting type