Answer: A) chemical - gas produced 
Explanation: Physical change is a process in which there is no change in chemical composition of the substance.
Chemical change is a process in which there is a change in chemical composition of the substance.
Chemical process is accompanied by following changes
1. Change in color
2. Absorption or release of energy
3. Production of gas
4. Formation of precipitates.
Thus a chemical reaction is happening on mixing baking soda 
 and vinegar
 and vinegar 
 , there is production of
, there is production of 
 which expanded the balloon.
 which expanded the balloon. 
