Okay, let's tackle this question about temporary water hardness. The question is asking how to remove temporary water hardness. First, I need to recall what temporary water hardness is. From what I remember, water hardness is due to the presence of calcium and magnesium ions. There are two types: temporary and permanent. Temporary hardness is caused by the bicarbonates of calcium and magnesium, right? So, when water is heated, these bicarbonates decompose into carbonates, which precipitate out as insoluble calcium carbonate and magnesium carbonate. That's why boiling the water removes temporary hardness.

Now, looking at the possible answer options. The correct answer should be boiling. Let me check the other options. If the options include adding lime (calcium hydroxide), that's for permanent hardness. Chlorination is for disinfection, not hardness removal. Distillation might remove both types but isn't a typical method for temporary hardness. So the correct answer is boiling. The key here is understanding the difference between temporary and permanent hardness and the methods to remove each. A clinical pearl here is that temporary hardness is the only type that can be removed by boiling, so if the question mentions "temporary," boiling is the answer.

**Core Concept**
Temporary water hardness arises from dissolved calcium bicarbonate (Ca(HCO₃)₂) and magnesium bicarbonate (Mg(HCO₃)₂). It is removed by heating, which decomposes bicarbonates into insoluble carbonates, CO₂, and water. Permanent hardness, caused by sulfates/chlorides, requires other treatments like ion exchange.

**Why the Correct Answer is Right**
Boiling water causes thermal decomposition of calcium bicarbonate into calcium carbonate (CaCO₃), CO₂, and H₂O. The insoluble CaCO₃ precipitates, reducing hardness. This method works specifically for temporary hardness, as permanent hardness requires chemical treatments like lime softening or ion-exchange resins.

**Why Each Wrong Option is Incorrect**
**Option A:** Chlorination disinfects water but does not remove hardness.
**Option B:** Distillation removes all solutes but is impractical for large-scale use and targets both temporary/permanent hardness.
**Option C:** Adding sodium carbonate (washing soda) removes permanent hardness by precipitating Ca²⁺/Mg²⁺ as carbonates but is not specific to temporary hardness.

**Clinical Pearl / High-Yield Fact**
Remember: **Boiling removes temporary hardness only**. For permanent hardness, use lime softening (Ca(OH)₂) or ion-exchange resins. A classic exam trap is confusing distillation with boiling—distillation is universal but inefficient.

**Correct Answer: D. Boiling**

✓ Correct Answer: D. Boiling