Final answer:
The least reliable method of determining urine specific gravity is the use of chemical reagent strips, as they are more prone to variability and human interpretation errors.
Step-by-step explanation:
The least reliable method for determining urine specific gravity among the options provided is B) Chemical reagent strips. Chemical reagent strips, often used for rapid urinalysis, can be subject to variability due to factors such as timing and interpretation of the color change. This method relies on a colorimetric reaction, where the strip changes color based on the concentration of solutes in the urine, which is then compared to a color chart. In contrast, refractometry, hydrometry, and the use of a urinometer are more direct methods. Refractometry measures the bending of light as it passes through the urine sample, hydrometers float in the liquid to provide a density reading, and the urinometer is a type of hydrometer specifically designed for urine. Each of these is considered more reliable due to their more precise nature and less susceptibility to human interpretation errors.