Question

when we open the cap of a drink, why does excess of bubble come out

Answer 1

 When the pressure is released by opening the soda container, the liquid cannot hold as much carbon dioxide, so the excess bubbles out of the solution.

Answer 2

Due to the liberation of carbondioxide cominf the carbonated or soda water. the prsseure of the soda bottle is very high comparing to the pressure of outside . so when the bottle is opened the excess pressure tends to come out and carbondioxide is released in the form of bubbles.