Answer:
B) a chemical change .
Step-by-step explanation:
There will be no chemical reaction when the gases ammonia and carbon dioxide are mixed together . But when there is presence of ammonium hydroxide , chemical reaction takes place between carbon dioxide and ammonium hydroxide resulting into the formation of ammonium carbonate as follows
2NH₄OH + CO₂ =( NH₄)₂CO₃ + H₂O.
The growth of white crystals inside the bottle indicates the presence of ammonium carbonate .
So it is a chemical change .