Which of the following is incorrect regarding ultraviolet rays?

Options

A. Cause death of micro organisms
B. Prolonged exposure cause skin cancer
C. They are the rays of visible spectrum
D. Help to convert sterols into vitamin D

Answer

To determine which statement regarding ultraviolet rays is incorrect, we need to analyze each provided statement based on our understanding of ultraviolet (UV) rays.

### Step-by-Step Solution:

1. **Understanding Ultraviolet Rays**:
- Ultraviolet rays are a form of non-ionizing radiation emitted by the sun and certain artificial sources. They are part of the electromagnetic spectrum.

2. **Benefits of Ultraviolet Rays**:
- UV rays play a crucial role in the synthesis of vitamin D in the human body. This is a beneficial effect of UV exposure.

3. **Harmful Effects of Ultraviolet Rays**:
- Overexposure to UV rays can lead to health risks, including skin cancer. This indicates that while UV rays have benefits, they can also be harmful.

4. **Effects on Microorganisms**:
- UV rays are known to kill microorganisms, which is why they are often used in sterilization processes.

5. **Visibility of Ultraviolet Rays**:
- UV rays are not visible to the human eye. This is a key characteristic of ultraviolet radiation.

6. **Analyzing the Statements**:
- Now, let’s evaluate the given statements:
- **Statement A**: "Cause death of microorganisms." (Correct)
- **Statement B**: "Prolonged exposure causes skin cancer." (Correct)
- **Statement C**: "They are the rays of visible spectrum." (Incorrect, as UV rays are not visible)
- **Statement D**: "Help to convert T-rolls into vitamin D." (Correct, assuming "T-rolls" refers to a typo and means "T-cells" or similar)

7. **Conclusion**:
- The incorrect statement regarding ultraviolet rays is **Statement C**: "They are the rays of visible spectrum."

### Final Answer:
The answer is **Statement C**: "They are the rays of visible spectrum."

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