The SI unit of heat energy is
Joule
Explanation of correct answers.
Option D: Heat is a form of energy, and therefore its SI unit is the joule (J)
Explanation of incorrect answers.
Option A and Option B: kilocalorie (kcal), Calorie, and BTU are other units of heat.
Option C: Degree Celsius is the unit of temperature.
Hence, option(D) is the correct answer.