Which of the following is a major environmental problem in heavily industrialized regions?

Acid rain is a major environmental problem in heavily industrialised regions. It forms when sulphur dioxide (SO₂) and nitrogen oxides (NO_x) released from the burning of fossil fuels in factories, power plants, and vehicles react with water vapour, oxygen, and other chemicals in the atmosphere to form sulphuric acid and nitric acid. These acids then fall to the ground as acidic precipitation (rain, snow, fog, or dry deposition).

Acid rain causes widespread environmental damage in industrialised areas and their downwind neighbours:

• It corrodes buildings, monuments, and metal structures.
• It acidifies lakes and rivers, killing aquatic life.
• It damages forests by leaching nutrients from the soil and harming leaves.
• It degrades soil quality, reducing agricultural productivity.

Accelerated erosion and frost damage are not specifically linked to heavy industrialisation. Water pollution can occur in industrial areas but is a broader problem not unique to the most heavily industrialised regions. Acid rain, by contrast, is directly and characteristically caused by the high concentration of industrial emissions that define heavily industrialised regions.