Concept:Temporary hardness is caused by soluble hydrogencarbonates of calcium and magnesium, formed when acidic rainwater reacts with carbonate deposits.
Explanation:Rainwater absorbs dissolved carbon(IV) oxide from the atmosphere, forming a weak carbonic acid solution.
This acidic water flows over underground deposits of calcium carbonate,
CaCO3.
The reaction produces soluble calcium hydrogencarbonate, which remains dissolved in the water as temporary hardness.
The chemical equation is:
CaCO3+CO2+H2O→Ca(HCO3)2Magnesium and calcium sulfates, such as
Na2SO4 and
CaSO4, cause permanent hardness, not temporary hardness.
Sodium carbonate does not produce temporary hardness in this way.
Therefore, the deposit involved must be
CaCO3.
Answer:A.
CaCO3