Set of elements known as chalcogens is :
1) O, S, Se,
2) CI, Br, I
3) N, P, S
4) C, Si, Ge

Options

A. O, S, Se,
B. CI, Br, I
C. N, P, S
D. C, Si, Ge

Answer

To solve the question regarding the set of elements known as chalcogens, we need to identify which option contains only chalcogen elements. Here’s a step-by-step solution:

### Step 1: Understand the Definition of Chalcogens
Chalcogens are elements that belong to Group 16 of the periodic table. The name "chalcogen" comes from the Greek words for "ore" and "to generate," indicating that these elements often form ores.

### Step 2: Identify the Chalcogen Elements
The elements classified as chalcogens include:
- Oxygen (O)
- Sulfur (S)
- Selenium (Se)
- Tellurium (Te)
- Polonium (Po)

### Step 3: Analyze Each Option
Now, let's evaluate each option provided in the question:

1. **O, S, Se**: This option contains oxygen, sulfur, and selenium, which are all chalcogens.
2. **Cl, Br, I**: This option contains chlorine, bromine, and iodine, which are halogens (Group 17).
3. **N, P, S**: This option contains nitrogen, phosphorus, and sulfur. While sulfur is a chalcogen, nitrogen and phosphorus are part of the nitrogen family (Group 15).
4. **C, Si, Ge**: This option contains carbon, silicon, and germanium, which are part of Group 14 (carbon family).

### Step 4: Conclusion
From the analysis, the only option that contains only chalcogen elements is:
**Option 1: O, S, Se**

### Final Answer
The set of elements known as chalcogens is: **O, S, Se (Option 1)**.

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