Amorphous silica, SiO2, has a density of about 2.2 g/cm3, whereas the density of crystalline quartz, another form of SiO2, is 2.65 g/cm3 . Which of the following statements is the best explanation for the difference in density
(a) Amorphous silica is a network-covalent solid, but quartz is metallic.
(b) Amorphous silica crystallizes in a primitive cubic lattice.
(c) Quartz is harder than amorphous silica.
(d) Quartz must have a larger unit cell than amorphous silica. (e) The atoms in amorphous silica do not pack as efficiently in three dimensions as compared to the atoms in quartz.

E. The atoms in amorphous silica do not pack as efficiently in three dimensions as compared to the atoms in quartz.

Explanation:

Quartz is a crystalline structure with a lattice which is very compact and produces flat faces that align with one another causing high density.

Silica has covalent bonding and forms a network structure. Silica, SiO2 is an amorphous solid and does not posses the same lattice or crystalline structure as Quartz, making it less dense.

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.