Which of the following is incorrect

Options

A. Enthalpy (numerical value) of physisorption is greater than that of chemisorption
B. Physisorption is not very specific but chomisorption is highly specific
C. Chemisorption takes place at relatively high temperatures
D. In physisorption generally multi-molecular layers are formed on the adsorbent

Explanation

To determine which statement is incorrect regarding the concepts of physisorption and chemisorption, we will analyze each statement step by step.

### Step 1: Analyze the first statement
**Statement:** "Enthalpy numerical value of physisorption is greater than that of chemisorption."

- **Explanation:** The enthalpy change associated with physisorption is typically lower than that of chemisorption. The values for physisorption range from about 20 to 40 kJ/mol, while for chemisorption, it ranges from 200 to 400 kJ/mol. Therefore, this statement is incorrect.

### Step 2: Analyze the second statement
**Statement:** "Physisorption is not very specific but chemisorption is highly specific."

- **Explanation:** This statement is correct. Physisorption occurs due to van der Waals forces, which are universal and do not favor any particular gas. In contrast, chemisorption involves the formation of chemical bonds, which is specific to certain reactants. Thus, this statement is true.

### Step 3: Analyze the third statement
**Statement:** "Chemisorption takes place at relatively high temperature."

- **Explanation:** This statement is also correct. Chemisorption requires sufficient activation energy to form chemical bonds, which typically occurs at higher temperatures compared to physisorption. Therefore, this statement is true.

### Step 4: Analyze the fourth statement
**Statement:** "In physisorption, generally multi-molecular layers are formed on the adsorbent."

- **Explanation:** This statement is correct. Physisorption can lead to the formation of multiple layers of adsorbate on the adsorbent surface, while chemisorption usually results in a unimolecular layer. Thus, this statement is true.

### Conclusion
After analyzing all statements, we find that the first statement is the only incorrect one. Therefore, the answer to the question is:

**Answer:** The incorrect statement is: "Enthalpy numerical value of physisorption is greater than that of chemisorption."

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