Which of the following is often used to control corrosion in drinking water systems?

Calcium hydroxide is commonly used to control corrosion in drinking water systems because it helps to increase the pH of the water, which can reduce the solubility of metals like lead and copper that may leach from pipes. By raising the pH, calcium hydroxide can create a more stable water chemistry, thereby minimizing the potential for corrosive conditions that lead to metal leaching into the drinking water supply.

When the pH of water is low (acidic), it is more corrosive to plumbing and pipe materials, leading to a greater tendency for these materials to dissolve into the water. By adjusting the water's chemistry with calcium hydroxide, utilities can maintain a safer and more stable drinking water environment, protecting both the infrastructure and public health.

The other options, while important in various water treatment processes, do not primarily serve the purpose of corrosion control in the same way as calcium hydroxide does. For example, ozone is primarily used for disinfection, ferrous sulfate is used for coagulation and as a source of iron, and chlorine is typically used as a disinfectant to kill pathogens. Their roles do not directly address the persistent challenge of corrosion in drinking water systems.