Question $3(20$ points$)$

A slit of variable width illuminated by light of wavelength $$ is widened until the first order diffraction minimum moves out to a distance infinitely far away from the brightest location in the central maximum. In terms of the wavelength, the width of the slit is then

$\frac{}{2}$

$$

$3\frac{}{2}$

$2$

$3$