Which of the following is treated with chlorine to obtain bleaching powder?

Options

A. dilute solution of `Ca(OH)_2`
B. concentrated solution of `Ca(OH)_2`
C. dry CaO
D. dry slaked lime

Explanation

To determine which substance is treated with chlorine to obtain bleaching powder, we follow these steps:

### Step 1: Understand what bleaching powder is
Bleaching powder is a chemical compound with the formula Ca(OCl)₂, also known as calcium oxychloride. It is commonly used as a bleaching agent and disinfectant.

### Step 2: Identify the precursor to bleaching powder
Bleaching powder is produced by the reaction of chlorine gas with dry slaked lime. Dry slaked lime is chemically represented as Ca(OH)₂.

### Step 3: Describe the reaction
When chlorine gas (Cl₂) is passed through dry slaked lime (Ca(OH)₂), a reaction occurs that produces bleaching powder (Ca(OCl)₂) along with the release of water (H₂O). The reaction can be summarized as follows:

\[ \text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{H}_2O \]

### Step 4: Identify the correct option
Given the information, the correct option that is treated with chlorine to obtain bleaching powder is **dry slaked lime (Ca(OH)₂)**.

### Final Answer
The substance that is treated with chlorine to obtain bleaching powder is **dry slaked lime (Ca(OH)₂)**.

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