............... rays are used in detecting fake currency and diamonds.

Options

A. UV
B. IR
C. Green
D. Blue

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question:** The question asks which type of rays are used to detect fake currency and diamonds.

2. **Identifying the Options:** The options provided are ultraviolet, infrared, green, and blue rays.

3. **Analyzing the Behavior of Materials:** It is known that certain materials exhibit specific behaviors when exposed to different types of rays. For instance, some materials fluoresce or change color under ultraviolet (UV) light.

4. **Application to Currency and Diamonds:**
- **Fake Currency Detection:** When ultraviolet rays are directed at currency notes, genuine notes will often fluoresce or show specific patterns (like a green strip) that fake notes do not exhibit.
- **Diamond Detection:** Similarly, diamonds can also exhibit unique fluorescence under UV light, helping to distinguish genuine diamonds from synthetic or fake ones.

5. **Conclusion:** Since both fake currency and diamonds can be effectively detected using ultraviolet rays, the correct answer to the question is **ultraviolet rays**.

**Final Answer:** Ultraviolet rays are used in detecting fake currency and diamonds.

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