Methane and oxygen are reactants because they are the substances we start with. They are on the side of the equation that the arrow is pointing away from.
Carbon dioxide and water are products because they are the new substances that are the yields of the equation. They are on the side of the equation that the arrow is pointing towards.
When sulfur dioxide combines with water and air, it forms sulfuric acid, which is the main component of acid rain. Acid rain can: cause deforestation. acidify waterways to the detriment of aquatic life