Which chemicals are known to raise pH in water?

The correct response highlights the use of Soda Ash (sodium carbonate) and Caustic Soda (sodium hydroxide) as effective means to raise pH in water. Soda Ash is a common chemical used in water treatment to adjust pH levels because it is a strong alkaline substance that effectively reacts with water to increase its pH when added. On the other hand, Caustic Soda is also a powerful alkaline agent that directly increases the pH levels by dissociating in water to produce hydroxide ions, thus making the water more alkaline.

In contrast, other choices include compounds that do not significantly raise pH or may have a neutral or even lowering effect on it. For example, Chlorine is primarily used for disinfection and can affect pH but is not used specifically for raising it. Similarly, Calcium Sulfate and Potassium Chloride tend to have neutral effects on pH within typical ranges of water treatment. Alum is primarily used as a coagulant, which can stabilize or slightly lower pH depending on the water chemistry. Lime, while capable of raising pH, is paired with alum in that option, which complicates its effectiveness in this context.