Answer:
From the information provided, it seems likely that substance A is an acid, and substance B is a carbonate. The fact that mixing the two substances results in bubbles or effervescence, and that a clear solution is formed, suggests that a chemical reaction is taking place.
Acids and carbonates react together to form a salt, water, and carbon dioxide gas. The reaction is as follow:
Acid + Carbonate → Salt + Water + Carbon Dioxide
The carbon dioxide gas forms bubbles in the solution and causes effervescence, and the clear solution formed is due to the fact that both the acid and the carbonate have reacted together to form the salt and water. This reaction is acid-base neutralization reaction as the acid and base will neutralize each other.
As for the acid, since it is said that B gives pH 3 solution after dissolved, it can be inferred that it is not an acid, otherwise it would be acidic. Therefore A which is insoluble is the acid.
As for the gas given off, it's Carbon dioxide.
Step-by-step explanation: