Question

Which of following forces is responsible for physisorption ?

• A. Coulombic force
• B. Electrostatic force
• C. London force of dispersion
• D. Hydrogen bonding

Hint:

Physisorption involves weak van der Waals forces, namely London dispersion forces.

Answer 1

The Correct Option is C

Step 1: Understand the concept
Adsorption can be physical (physisorption) or chemical (chemisorption). They differ in the type of force between the adsorbate and the surface.

Step 2: Physisorption forces
Physisorption is caused by weak van der Waals forces, mainly London dispersion forces. These forces act between any molecules, so the process is non-specific and reversible, with a low enthalpy of about 20-40 kJ/mol.

Step 3: Compare with chemisorption
Chemisorption involves chemical bonds, which are strong, specific and need activation energy, with an enthalpy of 80-240 kJ/mol.

Step 4: Why not the others
Coulombic and electrostatic forces act between ions and are typical of ionic bonds, and hydrogen bonding needs special groups (N-H, O-H, F-H). None of them is the general force that causes physisorption.

Final Answer:
Physisorption arises from London dispersion forces. This is option (C). \[ \boxed{\text{(C) }\text{London force of dispersion}} \]