Properties of Solids Practice Test

A solid is made of an extended 3D network of covalent bonds between silicon and oxygen atoms (no discrete molecules or ions). Which property is most consistent with this type of solid?

A solid is composed of $\text{Na}^+$ and a large polyatomic anion. The solid is hard and crystalline, and it shatters when struck. Which observation would best support classifying this solid as ionic rather than metallic?