Sodium is a highly reactive element and is not found in its free state in nature due to its high reactivity. It readily reacts with other elements and compounds, forming various salts and minerals. Sodium is commonly found in the Earth's crust and in seawater as compounds, such as sodium chloride (table salt).

Methane is the gas that can cause explosions in coal mines. Methane is a highly flammable gas, and when it accumulates in high concentrations in confined spaces like coal mines, it poses a significant risk. Methane explosions can occur if the gas comes into contact with an ignition source, such as a spark or flame, leading to a dangerous explosion. That's why proper ventilation and safety measures are crucial in coal mines to prevent methane buildup and potential explosions.