Substance Z is 46.7 % Si and 53.3 % O by mass. It has a melting point of 1 610 °C, is extremely hard, and does not conduct electricity in the solid or molten state. Which classification of Z is most strongly supported by these observations?
a) Ionic lattice made of Si4+ and O2− ions whose strong electrostatic attractions give the substance its hardness and high melting point.
b) Network-covalent solid in which each Si atom is tetrahedrally bonded to O atoms, forming an extended SiO2 lattice.
c) Molecular solid consisting of discrete SiO2 molecules held together only by London dispersion forces.
d) Ionic compound of Si4+ and O2− ions that remains non-conductive when molten because the ions’ high charges keep them from moving freely.