Hcl gas is introduced at one end of the tube, and simultaneously nh3 gas is introduced at the other end. when the two gases diffuse through the cotton plugs down the tube and meet, a white ring appears due to the formation of nh4cl(s). why is this?

When the two gases are mixed, the ammonium chloride precipitates in the tube walls.

Explanation:

This is the reaction:

HCl (g)  +  NH₃(g)  →  NH₄Cl (s) ↓

As the product formed is solid at room temperature, a suspension is first formed in the internal air of the tube that appears as a cloud. Afterwards it finally precipitates into the walls forming a white layer

both adhesion and cohesion are attractions.

they are different in that adhesion is the force of attraction between the molecules of two different substances, whereas cohesion is the force of attraction between molecules of the same substance.

possible examples include capillary action, in which the adhesion between water and glass causes the water to rise in a narrow tube against the force of gravity.

because of hydrogen bonding, water is extremely cohesive.

this causes molecules on the surface of water to be drawn inward, which is why drops of water form beads on smooth surfaces.

hope this .