What is the measurement of energy required to heat 1 pound of water from 39°F to 40°F?

The measurement of energy required to heat 1 pound of water from 39°F to 40°F is expressed in BTUs, which stand for British Thermal Units. A BTU is defined as the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. This makes BTU the appropriate unit of measurement for this specific scenario involving water temperature change.

In the context of heating water, BTUs are commonly used, especially in applications related to heating systems, air conditioning, and other energy-related issues where water is the medium being heated or cooled. The other units listed, such as Joules, Kilojoules, and Calories, are different measures of energy but are not specifically tailored for heating water in pounds and degrees Fahrenheit. For instance, a Joule is the SI unit of energy and a Calorie is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius, which is not directly applicable in this case of pounds and Fahrenheit. Thus, BTU is the most suitable answer.