Substance $W$ shows the physical properties listed below. Melting point $= 2072^\circ\text{C}$ Boiling point $= 2980^\circ\text{C}$ Electrical conductivity: poor (solid), good (liquid), insoluble in water. What substance is $W$?
- Aaluminium oxide
- Biron
- Csilicon dioxide
- Dsodium fluoride