Answer
The second order.
Work Step by Step
Use equation 24–4 to find the order.
The maximum angle is 90 degrees.
The number of slits per cm is the reciprocal of the slit width (measured in cm).
$$d sin \theta = m \lambda $$
$$m=\frac{d sin \theta}{ \lambda }$$
$$=\frac{(\frac{1}{6500}cm)(sin 90^{\circ})}{6.33\times10^{-5}cm}$$
$$=2.43$$
The second order is the highest spectral order that can be seen.
