How is the 20% evaporated point scientifically determined?

The scientifically accepted method for determining the 20% evaporated point is through ASTM D 86 distillation methods. This method involves heating a sample of liquid and measuring the temperature at which 20% of the sample has evaporated. ASTM D 86 provides standardized procedures for the distillation of petroleum products and helps in establishing accurate boiling point ranges. This precise measurement is crucial in various applications, such as understanding the volatility of fuels and designing safe handling protocols.

The other choices lack the rigor and precision needed for scientific determination. Using an arbitrary temperature scale does not provide a standard or universally accepted reference for measurement. The boiling process at standard temperature could lead to inconsistencies because actual boiling points can vary with pressure and composition. Rather than relying on empirical observations or estimations, the ASTM D 86 method provides a systematic and replicable procedure, ensuring reliability in results.