Science — AI-generated practice question

In reality, half a water molecule does not exist independently. The formula CaSO₄·½H₂O means that two formula units of CaSO₄ share one water molecule. In other words, for every 2 units of calcium sulphate, only 1 molecule of water is present as water of crystallisation. The formula is written this way as a simplified representation.

Source: Chapter 2, Section 2.4.4 – Are the Crystals of Salts really Dry?

• Examiners expect two key points: (1) half a water molecule cannot exist alone, and (2) the actual meaning — 2 CaSO₄ units share 1 H₂O molecule.
• Quoting directly from the textbook explanation is safest here.
• Do not write a long paragraph; two clear sentences covering both points are enough for 2 marks.