The upgrade that allows Mario to break stone or cracked-looking blocks in Paper Mario 64 is the Super Hammer. Mario obtains it during the Dry Dry Ruins portion of the adventure, after which he can smash tougher gray stone blocks that the ordinary Hammer cannot break.
The Super Hammer is the first major hammer upgrade in the game. It expands Mario’s exploration abilities as well as his combat options, letting him reach areas that were previously blocked. In battle, its stronger hammer attack can also deal more damage than the basic Hammer, depending on Mario’s action-command performance and equipped badges.
Paper Mario 64 uses several visually similar obstacle types, which causes frequent confusion. Ordinary yellow blocks require the standard Hammer, while stone blocks require the Super Hammer. Metal blocks are tougher still and require the later Ultra Hammer. Separately, walls and objects with visible cracks are generally associated with Bombette’s Bomb ability rather than a hammer upgrade.
Despite that terminology overlap, the quiz’s intended upgrade is the Super Hammer: it is the canonical early-game tool for breaking the gray, stone-like barriers that block Mario’s path.