A chemist studied the phenomenon of adsorption by putting blood charcoal in `KCL` solution. He observed difference in the behaviour with dilute `KCL` solution and with concentrated `KCL` solution. He also studied the adsorption of different gases on solid adsorbent and the effect of temperature on adsorption. He put forward a mathematical relationship relating `x//m` with equilibrium pressure.
Which of the following is correct ?

Options

A. Adsorption is always exothermic?
B. Adsorption is always endothermic.
C. Physical adsorption is endothermic whereas chemisorption is exothermic.
D. Chemical adsorption is endothermic whereas physical adsorption is endothermic

Explanation

To solve the question regarding the behavior of adsorption and the nature of the process, we can follow these steps:

### Step 1: Understand the Concept of Adsorption
Adsorption is the process where molecules from a gas or liquid adhere to a solid surface. It can be classified into two main types: physical adsorption (physisorption) and chemical adsorption (chemisorption).

### Step 2: Analyze the Observations Made by the Chemist
The chemist observed differences in adsorption behavior with dilute and concentrated KCl solutions. This suggests that the concentration of the solute can affect the extent and nature of adsorption.

### Step 3: Recall the Thermodynamics of Adsorption
Adsorption is generally associated with a decrease in surface energy. When molecules adhere to a surface, the residual forces at the surface decrease, leading to the release of energy in the form of heat.

### Step 4: Determine the Nature of Adsorption
- **Physical Adsorption**: Usually weak van der Waals forces are involved, and it is generally exothermic.
- **Chemical Adsorption**: Involves stronger chemical bonds and is also typically exothermic.

### Step 5: Conclude the Nature of the Process
Since both types of adsorption (physical and chemical) result in a decrease in surface energy and release heat, we conclude that adsorption is always an exothermic process.

### Step 6: Evaluate the Options
Based on the understanding that adsorption is exothermic, we can evaluate the options provided:
1. Adsorption is always exothermic (Correct)
2. Adsorption is always endothermic (Incorrect)
3. Physical adsorption is endothermic (Incorrect)
4. Chemical adsorption is endothermic (Incorrect)
5. Various physical adsorption is endothermic (Incorrect)

### Final Answer
The correct statement is: **Adsorption is always exothermic.**

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