Biodegradable wastes are substances that will decay quickly. Which list contains only non-biodegradable wastes?

The question states that "Biodegradable wastes are substances that will decay quickly." Therefore, non-biodegradable wastes are substances that do not decay quickly or take a very long time to decay.

• Biodegradable items include organic matter like food scraps, leaves, betel nut husks, coconut husks, and betel nut spittle, as these are natural materials that decompose relatively quickly.
• Non-biodegradable items include man-made materials like plastic, tins, metal scraps, and bottles (typically glass or plastic).

• A. Plastic, tins, metal scraps: All three items (plastic, metal tins, metal scraps) are non-biodegradable.
• B. Food scraps, plastics, betel nut husks: Food scraps and betel nut husks are biodegradable. Plastics are non-biodegradable. This list is incorrect.
• C. Betel nut spittle, bottles, plastics: Betel nut spittle is biodegradable. Bottles and plastics are non-biodegradable. This list is incorrect.
• D. Leaves, betel nut husks, coconut husks: All three items (leaves, betel nut husks, coconut husks) are biodegradable. This list is incorrect.

Option A is the only list that contains exclusively non-biodegradable wastes.

The final answer is $\text{A}$