An industrial furnace requires a structural support rod that can operate continuously at temperatures up to 1200∘C1200^\circ\text{C}1200∘C without melting or deforming, while also acting as an electrical insulator to prevent short-circuiting of the heating elements.
Which of the following substances is the most suitable material for this support rod based on its structure and properties?
Calcium chloride (CaCl2\text{CaCl}_2CaCl2), because its giant ionic structure gives it a high melting point and allows it to conduct electricity in the solid state.
Graphite, because its giant covalent structure gives it a very high sublimation point and its delocalised π\piπ-electrons make it a highly effective electrical insulator.
Silicon dioxide (SiO2\text{SiO}_2SiO2), because its giant covalent structure gives it a high melting point and the absence of mobile ions or delocalised electrons makes it an excellent electrical insulator.
Poly(tetrafluoroethene) (PTFE), because its strong carbon-fluorine covalent bonds allow it to remain structurally stable up to 1500∘C1500^\circ\text{C}1500∘C while acting as an electrical insulator.