Diffraction grating angles depend on wavelength and slit spacing Steps: - Recall the grating equation: $d \sin \theta = m \lambda$, where $d$ is slit spacing, $\lambda$ is wavelength, $\theta$ is diffraction angle, and $m$ is order. - For constant $\theta$, $d$ must adjust inversely with $\lambda$: longer $\lambda$ requires smaller $d$. - Screen distance affects spot positions but not angles $\theta$, which are fixed by the grating. - Increasing lines per unit length decreases $d$. Why B is correct: - Red light has longer $\lambda$ than green, so increasing lines per unit length decreases $d$, keeping $d / \lambda$ constant and thus $\theta$ unchanged per the grating equation. Why the others are wrong: - A: Blue light shortens $\lambda$, requiring larger $d$ for same $\theta$; screen distance does not affect angles. - C: Red light lengthens $\lambda$, but screen …