IV was the one with the whales. The one where they go back in time. You are probably thinking of III maybe. The Search for Spock after the genesis thing hit the planet in II. I think my two favorites are probably II and VI. Of the original ones anyway.
Yeah, it was IV. Remember, at the start of the film before they vote to return to earth and face court martial and end up traveling in time to save the whales, Spock is at the computer in a cave doing his reeducation when his mother comes in and persuades him to rejoin Kirk.
Ah, okay. I guess I don't remember that part, but I know I have seen every trek movie in the theater starting with wrath of Khan.