Answer
$2.05\times 10^{7}$
Work Step by Step
The wavelengths of laser can be precisely “tuned” to anywhere in the visible range—that is, in the range $450\;nm\lt\lambda\lt650\;nm$
Therefore the frequency range of the laser is
$\frac{3\times 10^{8}}{650\times10^{-9}}\;Hz\lt f\lt \frac{3\times 10^{8}}{450\times10^{-9}}\;Hz$
$\implies 4.62\times 10^{14}\;Hz\lt f \lt 6.67\times 10^{14}\;Hz$
The total frequency band=$(6.67-4.62)\times 10^{14}\;Hz=2.05\times 10^{14}\;Hz$
If every television channel occupies a bandwidth of 10 MHz, the number of channels can be accommodated within this wavelength rang is given by
$n=\frac{2.05\times 10^{14}}{10\times 10^{6}}=2.05\times 10^{7}$
Therefore, the number of channels can be accommodated within this wavelength rang is $2.05\times 10^{7}$
