Answer
The lower limit of the Brewster angle is $~~55.5^{\circ}$
Work Step by Step
On the graph in Figure 33-18, we can see that the index of refraction in quartz for light with a wavelength of $700~nm$ is $n = 1.456$
We can find the Brewster angle:
$\theta_B = tan^{-1}~\frac{n_2}{n_1}$
$\theta_B = tan^{-1}~\frac{1.456}{1.00}$
$\theta_B = 55.5^{\circ}$
The lower limit of the Brewster angle is $~~55.5^{\circ}$
