Which one of the following is non-biodegradable?

• a. DDT
• b. Vegetable peel
• c. Cardboard
• d. Bark of trees.

Among the options provided, the substance that is non-biodegradable is:

Identifying Non-Biodegradable Materials

Non-biodegradable materials are those that do not break down naturally in the environment. Let's look at each option:

• DDT: This is a pesticide that remains in the environment for a long time and does not decompose easily.
• Vegetable peel: This is organic waste that decomposes quickly.
• Cardboard: This material is biodegradable and breaks down over time.
• Bark of trees: This is also biodegradable as it comes from a natural source.

Thus, the correct answer is DDT, as it is the only option that is non-biodegradable.