Diffraction grating orders limited by observable angles Steps:

• Grating spacing d = 1/300 mm = 3.33 × 10^{-6} m ≈ 3 × 10^{-6} m.
• Wavelength λ = 600 nm = 6 × 10^{-7} m.
• Maximum order from d sin θ = m λ with sin θ ≤ 1 gives m ≤ d/λ ≈ 5.
• For m = 5, sin θ = 1 so θ = 90°, unobservable on screen; thus m_max = 4.
• Total bright spots = 2 m_max + 1 (symmetric about m = 0) = 9. Why D is correct:
• The 9 spots arise from m = -4 to +4, as higher orders at 90° are excluded per the grating equation and practical visibility. Why the others are wrong:
• A. 4: Counts only positive orders up to m = 4, ignoring symmetry and center.
• B. 5: Counts orders from m = 0 to 4 on one side only.
• C. 8: Counts orders from m = ±1 to ±4, excluding central m = 0 maximum.

Final answer: D