Which one of the following statements is not correct?

Statement 4 is incorrect because the density of ice is actually lower than that of liquid water. When water freezes, its molecules rearrange into a crystalline lattice structure held together by hydrogen bonds. This open hexagonal arrangement increases the space between molecules, causing a decrease in overall density [1]. Consequently, ice floats on water because the buoyant force exceeds the force of gravity. Statement 1 is correct; boiling occurs when a liquid's vapour pressure equals the ambient atmospheric pressure. Statement 2 is correct as water is a highly polar molecule capable of hydrogen bonding, allowing it to dissolve many substances. Statement 3 is also correct; permanent hardness is caused by dissolved salts such as magnesium chloride (MgCl2), calcium chloride (CaCl2), and sulfates like MgSO4 and CaSO4, which cannot be removed by simple boiling.

Sources

1. [1] https://www.swc.nd.gov/arb/news/atmospheric_reservoir/pdfs/2016_12%20-%20Ice%20Vs%20Water%20--%20Density%20Matters.pdf