Explanation:

- Granite

- A dense, hard rock.

- It sinks in water.

- Obsidian

- A glassy, volcanic rock.

- Has moderate density.

- It sinks in water.

- Pumice

- A volcanic rock filled with air bubbles.

- Extremely lightweight and porous.

- Floats in water.

- Slate

- A metamorphic rock.

- Dense and layered.

- It sinks in water.

Answer:

- The correct option is Pumice.

- It’s the only rock mentioned that floats due to its porous nature.