Which MARPOL Annex category indicates a major hazard to marine resources or human health?

• A. X
• B. Y
• C. Z
• D. OS

Answer: (A)

The important idea is how MARPOL Annex II classifies noxious liquid substances carried in bulk to guide discharge restrictions. Substances are put into four hazard categories: X, Y, Z, and OS. Category X signals the most severe danger to the environment and human health, so such substances are treated as major hazards and discharges are prohibited or highly restricted. Categories Y and Z indicate progressively lower levels of hazard, with corresponding restrictions, while OS covers substances not classified in X, Y, or Z and managed under other rules. Because a major hazard to marine resources or human health is associated with the highest category, that category is the correct choice.