What is the term for the heat required to warm one gram of liquid H2O by one Kelvin?

The term for the heat required to warm one gram of liquid H2O by one Kelvin is indeed the calorie. In thermodynamics, a calorie is defined specifically as the amount of heat needed to raise the temperature of one gram of water by one degree Celsius, which is equivalent to one Kelvin since the size of the degree is the same on both the Celsius and Kelvin scales. This specific heat capacity of water is a critical concept in physics and chemistry due to water's unique properties and its role in various biological and physical processes.

Joules, BTUs, and Watts are all related to energy and heat transfer but are measured differently. The joule is a more general unit of energy in the International System of Units and is defined in terms of work done. A BTU is a larger unit of heat energy used primarily in heating and cooling systems but is not defined in terms of changes in temperature of water specifically. A watt measures power, which is the rate of energy transfer, not a specific quantity of heat required to change the temperature of water. Thus, the calorie specifically pertains to the context of warming water, making it the correct answer.