Question

In physical adsorption, the gas molecules are held by solid surfaces through
(a) strong chemical forces
(b) van der waals’ forces
(c) metallic bonds
d) gravitational forces

Answer 1

In physical adsorption, the gas molecules are held by solid surfaces through strong chemical forces because adsorption when interaction between the solid and the condensed molecules are strong as contrasted with physical adsorption.
I hope it will be helpful.

Answer 2

In physical adsorption, the gas molecules are held byVAN DER WALL FORCE.

FOR EXAMPLE:

one of van der Waals' three forces is dipole dipole force. For example, in HCl  the  Hydrogen and Chlorine atoms are polar. while the Chlorine atom have an extra electron, that is from the hydrogen .

so your answer is option b :)