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? |
|---|---|---|---|---|
| P | 1455 | 2913 | Yes | Yes |
| Q | -182 | -161 | No | No |
| R | 605 | 1137 | No | Yes |
a.[3]
Identify which substance (P, Q, or R) is a simple covalent substance and explain your choice using evidence from the table.
b.[1]
State the physical state of substance Q at room temperature (20degC).
c.[2]
The diagram below represents the arrangement of atoms in a solder alloy:
Determine the simplest whole-number ratio of tin to lead atoms shown in this alloy diagram.
d.[3]
Explain why solder is harder than pure tin.