The correct answer is option 1. Hard water does not give lather with soap because it contains calcium (Ca) and magnesium (Mg) ions which react with the soap to form insoluble precipitates. Soap molecules have a polar end that attracts dirt and a non-polar end that attracts water. When soap is mixed with soft water (water that does not contain high levels of calcium and magnesium ions), the soap molecules can easily form a lather by dissolving in the water and trapping dirt particles within the lather.

However, in hard water, the calcium and magnesium ions react with the soap molecules, causing them to separate and form insoluble compounds, commonly known as soap scum. As a result, the soap is unable to dissolve properly in hard water and does not produce a significant lather. This can make it difficult to clean effectively with soap in hard water.

Alert - correct answer should be option 1.