What is the CGS unit of heat?

The CGS (Centimeter-Gram-Second) system unit of heat is the Calorie. Option A (Joule) is incorrect — Joule is the SI unit of heat, not the CGS unit. Though Joule is the internationally accepted unit, CGS system uses calorie. Option B (Watt) is incorrect — Watt is the unit of power (rate of energy transfer), not heat energy itself. 1 Watt = 1 Joule per second. Option C (Calorie) is CORRECT — In the CGS system, calorie is the standard unit of heat. One calorie is defined as the amount of heat required to raise the temperature of 1 gram of water by 1°C (from 14.5°C to 15.5°C). Option D (Kelvin) is incorrect — Kelvin is the SI unit of temperature, not heat. It is important to distinguish between the measurement of heat energy and temperature. Students preparing for SSC, UPSC, or Railway exams must remember: CGS unit = Calorie, SI unit = Joule, and the relationship 1 calorie = 4.186 joules.