The wavelength range of the visible spectrum extends from violet $(400 \, nm)$ to red $(750 \, nm).$ Express these wavelengths in frequencies $(Hz).$ $(1 \, nm = 10^{-9} \, m)$

Using the equation $v = \frac{c}{\lambda}$,where $c = 3.00 \times 10^{8} \, m \, s^{-1}$ is the speed of light.
For violet light $(\lambda = 400 \, nm = 400 \times 10^{-9} \, m)$:
$v = \frac{3.00 \times 10^{8} \, m \, s^{-1}}{400 \times 10^{-9} \, m} = 7.50 \times 10^{14} \, Hz$
For red light $(\lambda = 750 \, nm = 750 \times 10^{-9} \, m)$:
$v = \frac{3.00 \times 10^{8} \, m \, s^{-1}}{750 \times 10^{-9} \, m} = 4.00 \times 10^{14} \, Hz$
Thus,the range of the visible spectrum in terms of frequency is from $4.00 \times 10^{14} \, Hz$ to $7.50 \times 10^{14} \, Hz$.