If the red light is replaced by blue light, the outcome will be option 3: the diffraction pattern becomes narrower and crowded together.

Diffraction is the bending or spreading of waves as they pass through an aperture (such as a slit) or around an obstacle (such as a barrier). When light waves pass through a small slit or aperture, they diffract and create a pattern of light and dark bands called a diffraction pattern. The spacing between these bands depends on the wavelength of the light.

Red light has a longer wavelength compared to blue light. When red light is replaced by blue light, which has a shorter wavelength, the diffraction pattern becomes narrower and crowded together. This is because the smaller wavelength of blue light leads to a larger angle of diffraction, resulting in narrower bands and a closer spacing between them in the diffraction pattern.

Therefore, the correct answer is option 3: the diffraction pattern becomes narrower and crowded together.