**Core Concept**
Bleaching powder is a commonly used disinfectant for feces, especially in areas with limited access to modern sanitation facilities. The correct concentration is crucial to ensure effective disinfection without causing harm to the environment or human health. The standard concentration of bleaching powder for feces disinfection is typically 5%.

**Why the Correct Answer is Right**
The recommended concentration of 5% is based on the presence of 5% available chlorine, which is the active disinfectant component of bleaching powder. When 5% available chlorine is mixed with water, it effectively kills a wide range of pathogens, including bacteria, viruses, and protozoa. This concentration also minimizes the risk of chlorination byproducts, which can be harmful to the environment and human health.

**Why Each Wrong Option is Incorrect**
* **Option A:** Using a concentration higher than 5% can lead to excessive chlorination, resulting in the formation of toxic chlorination byproducts and potentially harming the environment and human health.
* **Option B:** Using a concentration lower than 5% may not be effective in killing all pathogens, particularly in areas with high levels of fecal contamination.
* **Option C:** Using a different type of disinfectant, such as phenol or cresol, may not be as effective as bleaching powder in disinfecting feces, especially in areas with limited access to modern sanitation facilities.
* **Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
When using bleaching powder for feces disinfection, it's essential to note that the correct concentration is 5% available chlorine, not 5% bleaching powder. This distinction is crucial to ensure effective disinfection without causing harm to the environment or human health.

**Correct Answer:** C. 5%