Which of the following material is bio-degradable?

1. A

   Glass bottle

   Glass bottle. Glass is a non-biodegradable inorganic material that does not decompose naturally in the environment over time.

2. B

   Plastic cups

   Plastic cups. Plastics are synthetic polymers derived from petroleum and are famously resistant to microbial degradation.

3. C

   Aluminium foril

   Aluminium foil. Aluminium is a metal and cannot be broken down by biological agents or natural microorganisms.

4. D

   Wool

   Wool. Wool is a natural protein fiber obtained from sheep and other animals, making it entirely biodegradable and easily decomposed by soil microorganisms.

Summary. Official key is (d) Wool. Glass bottles, plastic cups, and aluminium foil are inorganic or synthetic substances that persist in the environment for centuries without breaking down. Wool, being a natural animal protein, is broken down by microorganisms into harmless organic matter. This makes wool the only biodegradable material among the given choices. Understanding biodegradation helps distinguish natural organic waste from persistent synthetic pollutants.