The following statement relate to the adsorption of gases on a solid surface. Identify the incorrect statement among them :

Options

A. On adsorption decrease in surface energy appears as heat
B. Enthalpy of adsorption is negative
C. On adsorption, the residual forces on the surface are increased
D. Entropy of adsorption is negative

Answer

To solve the question regarding the incorrect statement about the adsorption of gases on a solid surface, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: "On adsorption, decrease in surface energy appears as heat."**
- When a gas is adsorbed onto a solid surface, the unstable surface particles experience a decrease in energy. This energy loss is released in the form of heat, indicating that the process is exothermic. Therefore, this statement is **correct**.

2. **Statement 2: "Enthalpy of adsorption is negative."**
- The enthalpy change during adsorption is negative because the process releases heat. A negative enthalpy indicates that the reaction is exothermic. Hence, this statement is also **correct**.

3. **Statement 3: "On adsorption, the residual forces on the surface are increased."**
- This statement is misleading. When a gas is adsorbed onto a surface, the interaction between the adsorbate (gas) and the adsorbent (solid surface) leads to a decrease in surface energy, not an increase in residual forces. The correct interpretation is that the forces between the adsorbate and adsorbent develop, leading to a stabilization of the surface, which actually reduces residual forces. Therefore, this statement is **incorrect**.

4. **Statement 4: "Entropy of adsorption is negative."**
- When a gas is adsorbed onto a surface, the movement of the gas molecules is restricted, leading to a decrease in randomness (or entropy). Since the degree of freedom of the particles decreases, the entropy of adsorption is indeed negative. Thus, this statement is **correct**.

### Conclusion:
The incorrect statement among the given options is **Statement 3: "On adsorption, the residual forces on the surface are increased."**