The table below shows information about four different substances.
| Substance | Melting point (∘C^{\circ}\text{C}∘C) | Appearance | Electrical conductor? |
|---|---|---|---|
| P | 108510851085 | shiny orange-brown solid | yes |
| Q | 115115115 | translucent flexible solid | no |
| R | 146514651465 | white crystalline powder | yes when dissolved in water |
| S | 585858 | white waxy solid | no |
Which of the substances is a polymer? Explain your answer.
Explain why polymers without cross-links can stretch and flex much more than polymers with cross-links.

Which substances from the table would be best to use to make each part of the screwdriver? Explain your answers.
Part A (outer handle grip):
Part B (metal shaft/tip):