Answer:
The effervescence I saw required vigorous stirring because when the acid reacts with bicarbonate such as sodium bicarbonate, carbondioxide gas is produced in the liquid which can be removed only by continuous stirring of the solution.
Step-by-step explanation:
When the acid reacts with sodium bicarbonate, carbonic acid and salts are produced. the carbonic acid decomposes into carbondioxide gas and water. this carbondioxide gas takes more time in releasing from the solution which requires continuous stirring of the solution.