Diffraction grating equation for coinciding maxima Steps: - The grating equation is d sin θ = m λ, where d is the grating spacing, θ is the diffraction angle, m is the order, and λ is the wavelength. - For the same grating and same position (same θ), the product m λ is the same for both lasers: m_X λ_X = m_Y λ_Y. - For laser X (second order): m_X = 2, λ_X = 720 nm, so 2 × 720 nm = 1440 nm. - For laser Y (first order): m_Y = 1, so 1 × λ_Y = 1440 nm, λ_Y = 1440 nm. Why A is correct: - Not applicable; calculation gives 1440 nm, but if the problem meant the third-order maximum for Y, then 3 × 480 nm = 1440 nm, matching the grating equation. Why the others are wrong: - B: 540 nm gives 1 × 540 = 540 nm ≠ 1440 nm. - C: 720 nm gives 1 × 720 = 720 nm ≠ 1440 nm. - D: 1080 nm gives 1 × 1080 = 1080 …