The molecular action of ultraviolet light is mainly reflected through:

Options

A. Destruction of hydrogen bonds in DNA.
B. Photodynamic action
C. Formational pyrimidine.
D. Formation of sticky metaphase.

Answer

### Step-by-Step Solution:

1. **Understanding Ultraviolet Light**: Ultraviolet (UV) light is a type of electromagnetic radiation that comes from the sun. It has shorter wavelengths than visible light and can have significant effects on biological molecules, particularly DNA.

2. **Role of the Ozone Layer**: The ozone layer in the Earth's atmosphere plays a crucial role in protecting living organisms from harmful UV radiation. It absorbs a significant portion of UV radiation, especially UV-B rays, which are more harmful.

3. **Effects of UV-B Rays**: When UV-B rays penetrate the atmosphere due to ozone depletion, they can cause damage to DNA. This damage occurs primarily through the destruction of hydrogen bonds in the DNA structure.

4. **DNA Mutation**: The destruction of hydrogen bonds in DNA can lead to mutations. Mutations are changes in the DNA sequence that can result in various health issues, including skin cancers and other diseases.

5. **Consequences of Increased UV Exposure**: Increased exposure to UV-B rays can lead to several health problems, including:
- Skin cancers due to DNA mutations.
- Thickening of the cornea and lens of the eye, leading to conditions such as cataracts and snow blindness.

6. **Conclusion**: The molecular action of ultraviolet light is mainly reflected through the destruction of hydrogen bonds in DNA, leading to mutations and various health issues.

### Final Answer:
The molecular action of ultraviolet light is mainly reflected through the destruction of hydrogen bonds in DNA.

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