Select the set having correct statements pertaining to the adsorption of a gas on a solid surface
(1) physisortion may transform into chemisorption at high temperature (2) chemisorption is more exothermic than physisortion , however it is very slow due to higher energy of activation
(3) Adsorption is always exothermic
(4) Physiosorption increase with increasing temperature but chemisorption decreases with increasing temperature

Options

A. 1,2
B. 2,3
C. 1,2,3
D. 1,2,4

Answer

To solve the question regarding the correct statements pertaining to the adsorption of a gas on a solid surface, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: Physisorption may transform into chemisorption at high temperature.**
- **Analysis:** This statement is correct. At high temperatures, the kinetic energy of the adsorbate molecules increases, allowing them to overcome the energy barrier for chemisorption. Thus, physisorption can indeed transform into chemisorption under these conditions.

2. **Statement 2: Chemisorption is more exothermic than physisorption; however, it is very slow due to higher energy of activation.**
- **Analysis:** This statement is also correct. Chemisorption involves the formation of stronger chemical bonds, making it more exothermic than physisorption, which is based on weaker van der Waals forces. However, chemisorption typically has a higher activation energy, which can make the process slower compared to physisorption.

3. **Statement 3: Adsorption is always exothermic.**
- **Analysis:** This statement is correct as well. Both physisorption and chemisorption release energy when the gas molecules adhere to the solid surface, making the process exothermic.

4. **Statement 4: Physisorption increases with increasing temperature, but chemisorption decreases with increasing temperature.**
- **Analysis:** This statement is incorrect. While physisorption may initially increase with temperature due to increased kinetic energy, it will eventually decrease as the thermal energy can break the weak van der Waals forces. Chemisorption, on the other hand, generally increases with temperature as more molecules can overcome the activation energy barrier.

### Conclusion:
The correct statements are 1, 2, and 3. Therefore, the answer to the question is that the set containing statements 1, 2, and 3 is correct.