Answer
$6$
Work Step by Step
The numbers of wavelengths of light $(\lambda=500\;nm)$ contained in a length
$n=\frac{L}{\lambda}$
If $\Delta t$ be the laser pulse, then the numbers of wavelengths of light $(\lambda=500\;nm)$ contained in such a pulse
$n=\frac{c\Delta t}{\lambda}$
or, $n=\frac{3\times10^{8}\times10\times10^{-15}}{500\times10^{-9}}$
or, $n=6$
Therefore, the numbers of wavelengths of light $(\lambda=500\;nm)$ contained in s the pulse is $6$
