Deflection angle ∝ charge-to-mass ratio; H ions are negative tritium ions (³H⁻, m ≈ 3m_p) Steps:

• Proton: q = +e, m = m_p, so q/m = +e/m_p, θ = 15°.
• H ion (³H⁻): q = -e, m = 3m_p, so q/m = -e/(3m_p) = -(1/3)(e/m_p).
• Ratio of (q/m)_H to (q/m)_proton = -1/3.
• Y = (-1/3) × 15° = -5°. Why B is correct:
• Negative tritium ions have q/m = -1/3 of protons' due to tripled mass and negative charge, per deflection proportionality. Why the others are wrong:
• A: -30° requires |q/m| twice protons' (e.g., q = -2e, m = m_p), impossible for H ions.
• C: +5° fits positive tritium ions (³H⁺), but H ions deflect negatively.
• D: +30° requires q/m twice protons' (e.g., q = +2e, m = m_p), not for H ions. Final answer: B