What physical quantity is the same for X- rays of wavelength `10^-10 m`,red light of wavelength `6800 A` and radio waves of wavelength `500 m` ?

Answer

To solve the question, we need to identify the physical quantity that remains constant for different types of electromagnetic waves, including X-rays, red light, and radio waves.

### Step-by-Step Solution:

1. **Identify the Wavelengths**:
- X-rays have a wavelength of \(10^{-10} \, \text{m}\).
- Red light has a wavelength of \(6800 \, \text{Å}\) (which is \(6800 \times 10^{-10} \, \text{m} = 6.8 \times 10^{-7} \, \text{m}\)).
- Radio waves have a wavelength of \(500 \, \text{m}\).

2. **Understand the Nature of Electromagnetic Waves**:
- All electromagnetic waves travel at the same speed in a vacuum, denoted as \(c\).

3. **Recall the Speed of Light**:
- The speed of light in a vacuum is approximately \(c = 3 \times 10^8 \, \text{m/s}\).

4. **Conclusion**:
- The physical quantity that is the same for X-rays, red light, and radio waves is the speed of light in a vacuum, which is \(c = 3 \times 10^8 \, \text{m/s}\).

### Final Answer:
The physical quantity that is the same for X-rays, red light, and radio waves is the speed of light, \(c = 3 \times 10^8 \, \text{m/s}\).