**Core Concept**
The permissible limit of arsenic in drinking water is a critical public health parameter, as excessive exposure to arsenic can lead to various health issues, including skin lesions, cardiovascular disease, and cancer. The World Health Organization (WHO) has set a guideline value for arsenic in drinking water to ensure safe consumption.

**Why the Correct Answer is Right**
The WHO permissible limit of arsenic in drinking water is set at 0.01 mg/L (10 μg/L) to minimize the risk of adverse health effects. This limit is based on the International Agency for Research on Cancer (IARC) classification of arsenic as a Group 1 carcinogen, indicating its potential to cause cancer in humans. Chronic exposure to arsenic above this limit can lead to the development of arsenicosis, a condition characterized by skin lesions, hyperpigmentation, and cardiovascular disease.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it is below the WHO permissible limit, which is set to ensure safe consumption.
* **Option B:** This option exceeds the WHO permissible limit, which can lead to adverse health effects, including cancer.
* **Option C:** This option is incorrect as it is not a recognized limit for arsenic in drinking water.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the WHO permissible limit of arsenic in drinking water is 0.01 mg/L (10 μg/L), and any level above this can increase the risk of adverse health effects. This is a critical consideration for public health officials and healthcare providers when assessing water quality and providing guidance to consumers.

**Correct Answer: B. 0.05 mg/L**