**Core Concept**
The Rideal-Walker Coefficient is a measure used to assess the efficiency of disinfectants. It is a quantitative indicator that evaluates the relative effectiveness of a disinfectant against a standard bacterium, typically *Salmonella cholerae-suis*. This coefficient helps in comparing the potency of different disinfectants and their ability to inactivate microorganisms.

**Why the Correct Answer is Right**
The Rideal-Walker Coefficient is calculated as the ratio of the concentration of the disinfectant required to inactivate the test organism to the concentration of a standard disinfectant, phenol, required to achieve the same level of inactivation. This coefficient is essential in determining the efficacy of disinfectants in various settings, such as hospitals and healthcare facilities. The test organism, *Salmonella cholerae-suis*, is specifically chosen for its susceptibility to disinfection and its ability to serve as a standard for comparison.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Rideal-Walker Coefficient is not used to assess the effectiveness of antibiotics, which are used to treat bacterial infections.
**Option B:** This option is incorrect because the coefficient is not related to the assessment of antiseptics, which are used to prevent infection on living tissues.
**Option C:** This option is incorrect because the coefficient is not used to evaluate the efficacy of vaccines, which are used to prevent infections by inducing immunity.

**Clinical Pearl / High-Yield Fact**
The Rideal-Walker Coefficient is an essential tool in the evaluation of disinfectants, and its use can help prevent the spread of infections in healthcare settings.

**Correct Answer:** C. The Rideal-Walker Coefficient is employed for the assessment of disinfectants.