Amethyst (silicon dioxide) is commonly used as a substitute for purple sapphire (aluminum oxide). Which of the following can be used to distinguish between amethyst and purple sapphire?

Identify whether the given is a physical property or chemical property

a. the density of silver is 10.49 g/mL

b. the hardness of silver is 2.5 Mohs scale

c. the reactivity of silver with acid

d. the melting point of silver is 961.8 °C