Final answer:
The 2. calorie (cal) is the common unit of heat energy required to raise the temperature of 1 gram of water by 1 degree Celsius. A single calorie is equal to 4.184 joules.
Step-by-step explanation:
The common unit of heat energy used to describe the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius is the calorie (cal). A calorie is defined as the energy needed to change the temperature of 1.00 g of water by 1.00°C. The SI unit of energy is the joule (J), and 1 calorie is equivalent to 4.184 joules. The kilocalorie (kcal), which is 1000 calories, is commonly used in reference to food energy; this is often referred to as a Calorie (with a capital C) on food packaging.
In contrast to the calorie, the watt (option 3) is a unit of power, not energy, and represents the rate at which energy is used. The kilogram (option 4) is a unit of mass, not energy. Therefore, the correct answer is option 2: Calorie.
SUMUP of the final answer: