Can someone help me do Q4 with explanation? I’m confused about the chemical equations and phrasing of the question.

The chemical equation being asked for is for the “softening” of hard water. In the problem, it explains what is done in order to soften the hard water. So you take that explanation, and turn it into a chemical equation. Your left side would be adding the sodium bicarbonate to the calcium bicarbonate filled hard water Ca(HCO3)2 + Na2CO3 - Then you would have to write your products. Since this is a double replacement chemical reaction, the products would be CaCO3 + NaHCO3. so then what you would go on to do is balance the equation, which would turn out to be simply Ca(HCO3)2 + Na2CO3 -> 2NaHCO3 + CaCO3. The ionic equation would be Ca^+1 + 2HCO3^-1 + 2Na^+1 + CO3^-1 -> 2Na^+1 + 2HCO3^-1 + Ca^+1 + CO3^-1. This is because of each individual element or compounds formal charge.

The answer is c) pyrite