## Core Concept
The question tests understanding of water hardness and its removal methods. Water hardness is caused by the presence of calcium and magnesium salts, which can be either temporary (bicarbonates) or permanent (sulfates, chlorides, and nitrates). Various methods can remove one or both types of hardness.

## Why the Correct Answer is Right
. (Boiling) is effective for removing temporary hardness by decomposing bicarbonates into insoluble carbonates, which precipitate out, and carbon dioxide, which escapes. However, it does not remove permanent hardness. On the other hand, . (lime and soda ash treatment) can remove both temporary and permanent hardness. Lime (calcium hydroxide) removes temporary hardness and some permanent hardness by precipitating calcium carbonate. Soda ash (sodium carbonate) removes permanent hardness by precipitating calcium and magnesium carbonates.

## Why Each Wrong Option is Incorrect
* **Option A:** (Filtration) - This method can only remove suspended particles and not dissolved salts causing hardness.
* **Option B:** (Activated carbon) - This method is used for removing organic compounds, chlorine, and unpleasant tastes and odors but not for removing water hardness.

## Clinical Pearl / High-Yield Fact
In medical settings, the type of water used can affect patient care, especially in dialysis. Hard water can cause scaling in pipes and equipment, while soft water may be corrosive. Understanding methods for water softening, like . (lime and soda ash treatment), is crucial for ensuring appropriate water quality.

**Correct Answer: C. **