Correct Answer - Option 1 : Bicarbonates
Hardness of water:
Hardness in water is that characteristic which prevents the formation of sufficient leather or foam, when such hard waters are mixed with soap. It is usually caused by the presence of calcium and magnesium salts present in water, which form scum by reaction with soap.
Hard waters are undesirable because they may lead to greater soap consumption, scaling of boilers, causing corrosion and incrustation of pipes, making foods tasteless, etc.
If bicarbonates and carbonates of calcium and magnesium are present in water, the water is rendered hard temporarily, as this hardness can be removed to some extent by simple boiling or to full extent by adding lime to the water. Such a hardness is known as temporary hardness or carbonate hardness.
When such waters are boiled carbon dioxide gas escapes out and the insoluble calcium carbonate gets precipitated. Magnesium carbonate being fairly soluble in water won’t get removed by boiling. The temporary hard waters, therefore do cause deposition of calcium scales in boilers.
Temporary hard water contains slightly soluble calcium bicarbonate, and this can be easily removed by boiling. On the other hand, permanent hardness is caused by dissolved calcium sulphate (which is not removed by boiling). The permanent hardness is removed by chemical treatment.