**Core Concept**
The frequency of a Wood's lamp is a crucial aspect of dermatological examination, particularly in diagnosing and managing various skin conditions. A Wood's lamp emits ultraviolet (UV) light, which helps in visualizing certain skin lesions, infections, and inflammatory conditions. The specific frequency of the UV light emitted is essential for effective diagnosis.

**Why the Correct Answer is Right**
The correct frequency of a Wood's lamp is typically in the range of 365 nanometers, which falls within the UVA spectrum. This specific wavelength is chosen because it is selectively absorbed by certain microorganisms and pigments, making it useful for diagnosing conditions like vitiligo, albinism, and fungal infections. The 365-nanometer wavelength is also less likely to cause phototoxicity and photoallergic reactions, making it a safer option for patients.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a valid frequency for a Wood's lamp. The frequency of a Wood's lamp is typically measured in nanometers, not megahertz or other units of measurement.
**Option B:** This option is incorrect because the frequency of a Wood's lamp is not in the range of 10-20 Hz, which is more commonly associated with low-frequency electromagnetic fields or electrical currents.
**Option C:** This option is incorrect because the frequency of a Wood's lamp is not in the range of 100-200 MHz, which is more commonly associated with radiofrequency (RF) energy used in medical treatments like diathermy.

**Clinical Pearl / High-Yield Fact**
When using a Wood's lamp, it's essential to remember that the specific frequency of the UV light emitted can affect the diagnostic accuracy and patient safety. Always check the manufacturer's specifications and follow proper guidelines for usage to ensure effective and safe diagnosis.

**Correct Answer:** 365 nanometers