Question

How can negative adsorption be adsorption since here the particles are accumulated even in the bulk ?

Answer 1

There are two types of materials diffusing one on another.

1. Adsorption: The concentration of adsorbate (the substance that is diffusing) is high in surface and less in bulk or vice versa. If the concentration of adsorpate is high in surface and less in bulk it is called as positive adsorption (The positive adsorption is only called as adsorption in short). If the concentration of adsorbate is less in surface and more in bulk it is called as negative adsorption. So there is concentration gradient in both cases.
2. absorption: The concentration of absorbed substance is uniform through out. This means the concentration is uniform in all areas in absorption.

So when there is change in concentration between surface and bulk it is adsorption only.