The table shows data about three different substances:
| Substance | Melting point (°C\degree\text{C}°C) | Boiling point (°C\degree\text{C}°C) | Conducts electricity as a solid? | Conducts electricity when molten? |
|---|---|---|---|---|
| X | 1085 | 2562 | Yes | Yes |
| Y | -114 | -85 | No | No |
| Z | 801 | 1413 | No | Yes |
a.[2]
Identify which substance (X, Y, or Z) is a simple covalent substance and explain your choice using evidence from the table.
b.[1]
State the physical state of substance Y at room temperature (20degC).
c.[2]
The diagram below represents the arrangement of atoms in a brass alloy:
Determine the simplest whole-number ratio of copper to zinc atoms shown in this alloy diagram.
d.[2]
Explain why brass is harder than pure copper.