Which of the following has negative temperature coefficient of resistance?

Options

A. Iron
B. Coppoer
C. Gas
D. Gold

Answer

To determine which of the given materials has a negative temperature coefficient of resistance, we can follow these steps:

### Step 1: Understand the Concept of Temperature Coefficient of Resistance
The temperature coefficient of resistance (α) indicates how the resistance of a material changes with temperature. If resistance increases with temperature, α is positive. If resistance decreases with temperature, α is negative.

### Step 2: Analyze Each Option
We will analyze each option provided to determine their temperature coefficients.

1. **Iron**:
- Iron is a good conductor of electricity.
- As temperature increases, the resistance of iron also increases.
- Therefore, the temperature coefficient of resistance for iron is positive.

2. **Copper**:
- Copper is also a good conductor of electricity.
- Similar to iron, as the temperature increases, the resistance of copper increases.
- Hence, the temperature coefficient of resistance for copper is positive.

3. **Gas**:
- Gases are generally poor conductors of electricity.
- When the temperature increases, the resistance of gases tends to decrease due to ionization, allowing current to flow more easily.
- Thus, the temperature coefficient of resistance for gases is negative.

4. **Gold**:
- Gold is a good conductor of electricity.
- As the temperature increases, the resistance of gold increases.
- Therefore, the temperature coefficient of resistance for gold is positive.

### Step 3: Conclusion
Among the options analyzed, only gases exhibit a negative temperature coefficient of resistance. Therefore, the correct answer is:

**Answer: Gas (Option C)**