Final answer:
Grinding quartz crystals into sand is a physical change because it does not alter the chemical composition of quartz, which remains as silicon dioxide.
Step-by-step explanation:
Grinding quartz crystals down to produce sand is an example of a physical change. This is because the process involves breaking down the crystals into smaller pieces without altering the chemical composition of the quartz. Quartz remains silicon dioxide (SiO2), regardless of whether it's in the form of a crystal or sand.
A chemical change would involve a change in the chemical composition, such as when iron rusts, or a candle wax burns, forming new substances. A physical change may involve a change in state or form, such as melting, freezing, or, in the case of quartz, grinding. Given the options, the answer to the question would be option 3, a physical change.