An aerospace sensor package contains a passive thermal fuse designed to protect electrical circuits. The fuse material must remain completely solid up to the maximum safe operating temperature of 55∘C55^{\circ}\text{C}55∘C, but must melt to become a liquid at 115∘C115^{\circ}\text{C}115∘C to break the connection. To prevent arcing through gaseous vapor, the material must not boil at 115∘C115^{\circ}\text{C}115∘C.
Based on the thermal properties in the table below, which substance is suitable for use as this thermal fuse?
| Substance | Melting point (∘C^{\circ}\text{C}∘C) | Boiling point (∘C^{\circ}\text{C}∘C) |
|---|---|---|
| P | 83 | 210 |
| Q | 125 | 290 |
| R | 70 | 105 |
| S | 15 | 165 |
Substance P
Substance Q
Substance R
Substance S
