Concept:The furring of kettles is caused by the decomposition of a soluble bicarbonate compound present in temporary hard water.
Explanation:Temporary hardness in water is due to dissolved calcium hydrogentrioxocarbonate (IV),
Ca(HCO3)2.
When this water is boiled in a kettle, the compound decomposes.
It forms insoluble calcium trioxocarbonate (IV),
CaCO3, which deposits as a hard scale inside the kettle.
This scale formation is known as furring of kettles.
Therefore, the compound originally present in the water that causes furring is calcium hydrogentrioxocarbonate (IV).
Answer:B. calcium hydrogentrioxocarbonate (IV)