(1) When baking soda (Sodium bicarbonate) is mixed with lemon juice(citric acid), bubbles are formed.
These bubbles are formed due to the evolution of carbon dioxide gas.
(2) The reaction between baking soda and lemon juice can be given as below:
Lemon juice + Baking soda → Carbon dioxide + other substances
(3) A chemical reaction is taking place which can't be reversed.
Since there is the formation of a new substance in this reaction, it is a chemical change.