Which of the following is used in the manufactures of bleaching powder and in softening of hard water ?

Options

A. NaOH
B. `Ca(OH)_2`
C. KOH
D. `Mg(OH)_2`

Explanation

To solve the question "Which of the following is used in the manufacture of bleaching powder and in softening of hard water?", we will follow these steps:

### Step 1: Identify the Compounds
We need to identify the compounds mentioned in the question. The question specifically asks about a compound that is used for two purposes: manufacturing bleaching powder and softening hard water.

### Step 2: Understand Bleaching Powder
Bleaching powder is chemically known as calcium oxychloride, with the formula Ca(OCl)₂. It is produced by the reaction of chlorine gas (Cl₂) with calcium hydroxide (Ca(OH)₂).

### Step 3: Reaction for Bleaching Powder
The reaction can be summarized as follows:
\[ \text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{H}_2\text{O} \]
This shows that calcium hydroxide is a key ingredient in the production of bleaching powder.

### Step 4: Understand Water Softening
Hard water contains dissolved minerals, primarily calcium and magnesium bicarbonates, which cause temporary hardness. Calcium hydroxide can be used to soften hard water by precipitating these bicarbonates.

### Step 5: Reaction for Softening Hard Water
When calcium hydroxide reacts with calcium bicarbonate (Ca(HCO₃)₂), it forms calcium carbonate (CaCO₃), which is insoluble and precipitates out:
\[ \text{Ca(OH)}_2 + \text{Ca(HCO}_3)_2 \rightarrow 2\text{CaCO}_3 \downarrow + 2\text{H}_2\text{O} \]
This reaction effectively removes the hardness from the water.

### Step 6: Conclusion
Based on the above information, we conclude that calcium hydroxide (Ca(OH)₂) is the compound used for both the manufacture of bleaching powder and the softening of hard water.

### Final Answer
The answer to the question is **Calcium Hydroxide (Ca(OH)₂)**.

---