Which of the following materials has an increase in resistance with temperature?

1. Analyze the question The question asks which material has a resistance that increases as temperature rises.

2. Explain the concept Resistance depends on how easily charge carriers move through a material.

• Metals: They have a fixed number of free electrons. When temperature rises, the metal ions vibrate more strongly, so the electrons collide with them more often. This hinders electron flow, so resistance increases. Metals have a positive temperature coefficient of resistance.
• Electrolytes: Heating frees more ions and makes the liquid less viscous, so ions move more easily. Resistance decreases.
• Semiconductors and insulators (for example, wood when dry): More charge carriers are freed at higher temperature, so resistance generally decreases.
• Pure water: It behaves like a weak electrolyte. More ions are produced at higher temperature, so resistance decreases.

3. Solution Checking each option:

• A. Water: resistance decreases with temperature ✗
• B. Metals: resistance increases with temperature ✓
• C. Wood: an insulator whose resistance decreases with temperature ✗
• D. Electrolyte: resistance decreases with temperature ✗

For metals, the relationship is R = R₀(1 + αΔT), where α is the positive temperature coefficient. R grows as T grows.

4. Answer The correct option is B. metals.

5. Exam tip Remember it this way: "Metals Mean More resistance when hot." Metals are the main materials whose resistance rises with temperature. Semiconductors, electrolytes, carbon and insulators go the other way, with resistance falling as they heat up.