How fast do X-rays travel in a vacuum and in air?
- Ain a vacuum $3.0 \times 10^6\,\text{m s}^{-1}$; in air $2.0 \times 10^6\,\text{m s}^{-1}$
- Bin a vacuum $3.0 \times 10^6\,\text{m s}^{-1}$; in air $3.0 \times 10^6\,\text{m s}^{-1}$
- Cin a vacuum $3.0 \times 10^8\,\text{m s}^{-1}$; in air $2.0 \times 10^8\,\text{m s}^{-1}$
- Din a vacuum $3.0 \times 10^8\,\text{m s}^{-1}$; in air $3.0 \times 10^8\,\text{m s}^{-1}$