Entropy (`S`) is a thermodynamic variable like pressure `P`, volume `V` and temperature `T`. Entropy of a thermodynamic system is a measure of disorder of molecular motion. Greater is disorder , greater is entropy. Change in entropy of a thermodynamic system is the ratio of heat supplied to absolute temperature.In an adiabatic reversible process, entropy remains constant while in any irreversible process entropy increases. In nature the processes are irreversible , therefore entropy of universe is continuoulsy increasing.
The unit of entropy in `S-I` system is -

Options

A. `"cal"//K`
B. `"joule"//"kg"`
C. `"joule"//"k"`
D. `"kilocal"//^(@)C`

Explanation

To determine the SI unit of entropy, let's break down the information provided step by step.

### Step-by-Step Solution:

1. **Understanding Entropy**:
- Entropy (`S`) is a thermodynamic variable that measures the disorder of molecular motion in a system. It is related to the amount of heat supplied to the system and the absolute temperature of the system.

2. **Change in Entropy Formula**:
- The change in entropy (`ΔS`) can be expressed as:
\[ ΔS = \frac{Q}{T} \]
where `Q` is the heat supplied to the system and `T` is the absolute temperature in Kelvin.

3. **Identifying Units**:
- In the SI system, the unit of heat (`Q`) is measured in joules (J).
- The unit of temperature (`T`) is measured in Kelvin (K).

4. **Calculating the Unit of Entropy**:
- From the formula for change in entropy, we can substitute the units:
\[ \text{Unit of } ΔS = \frac{\text{Unit of } Q}{\text{Unit of } T} = \frac{\text{J}}{\text{K}} \]
- Therefore, the unit of entropy in the SI system is joules per Kelvin (J/K).

5. **Conclusion**:
- The correct SI unit of entropy is **joules per Kelvin (J/K)**.