Which of the following substances can block some ultraviolet (UV) rays?

• A. ZnO (zinc oxide)
• B. H_2O (water)
• C. C_6H_{12}O_6 (glucose)
• D. NaCl (sodium chloride)

Answer: (A)

Verified step by step guidance

1. Understand that ultraviolet (UV) rays are a form of electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays.
2. Recognize that substances which can block or absorb UV rays typically have electronic structures or properties that allow them to interact with UV light, such as wide band gaps or the ability to absorb high-energy photons.
3. Consider the chemical nature of each substance: H_2O (water) is mostly transparent to UV, C_6H_{12}O_6 (glucose) is an organic molecule that does not strongly absorb UV, and NaCl (sodium chloride) is an ionic compound that is also mostly transparent to UV light.
4. ZnO (zinc oxide) is a semiconductor with a wide band gap, which allows it to absorb and block UV radiation effectively, making it a common ingredient in sunscreens and UV-blocking materials.
5. Therefore, identify ZnO as the substance capable of blocking some ultraviolet rays due to its electronic and structural properties.