Which environmental risk is not associated with the disposal of used motor oil from cars?

The correct answer is (c) Acid rain. While used motor oil can contribute to soil and water contamination, the release of harmful substances into the air, and the pollution of ecosystems, it is not directly linked to acid rain. Acid rain is primarily caused by the emission of sulfur dioxide and nitrogen oxides from industrial activities and vehicles, which react with water vapor in the atmosphere to form acidic compounds.