Which expression correctly defines moisture content as a percentage of water loss during drying?

• A. (W - D) / D × 100
• B. (D - W) / W × 100
• C. (W - D) / W × 100
• D. D / W × 100

Answer: (C)

Moisture content defined as a percentage of water loss during drying compares the amount of water removed to the original, wet weight of the sample. The water removed is the difference between the wet weight and the final dry weight, and you divide that by the original wet weight, then multiply by 100 to get a percent.

For example, if a sample weighs 500 g when wet and 420 g after drying, water lost = 500 − 420 = 80 g. The percent moisture lost relative to the original weight is 80/500 × 100 = 16%.

This definition specifically ties the moisture loss to the initial weight. Other formulations would measure different relationships (such as water lost relative to the dry weight, or dry weight as a fraction of the wet weight), which is not the same concept.