Explanation:

- Option 1: Hydrogen with oxygen can indeed explode, but hydrogen is rarely present in significant quantities in mines.

- Option 2: Methane with air is the correct answer. Methane (firedamp) is commonly found in coal mines. When it mixes with air, even a small spark can cause a dangerous explosion.

- Option 3: Oxygen with acetylene forms an explosive mixture, but acetylene is not typically found in mine atmospheres—it is more common in welding processes.

- Option 4: Carbon dioxide with methane does not form an explosive mixture; in fact, carbon dioxide can help suppress flames.