Among the following options the example of absorption is :

1.  Water on silica gel.

2.  Water on calcium chloride.

3.  Hydrogen on finely divided nickel.

4.  Oxygen on metal surface.

 
 
 
HINT: Water on calcium chloride is an example of absorption.
 
Explanation:
 
Absorption means penetration of adsorbate molecules into the bulk of the adsorbent e.g., water on calcium chloride. When water is spread over calcium chloride, water gets penetrate into bulk of the calcium chloride.