What is DDT among the following:

DDT stands for dichloro-diphenyl-trichloroethane. It is an organochlorine insecticide that was once widely used in agriculture and public-health programmes.

Key facts about DDT:
• It is highly stable and resists chemical, biological and photolytic degradation.
• Because it does not break down readily, it persists for many years in soil and water, bio-accumulates in the food chain and magnifies in higher trophic levels.
• Because of this persistence, DDT is classified as a persistent organic pollutant (POP) and is therefore termed a non-biodegradable pollutant.

Checking the options one by one:

Option A: Greenhouse gases are substances like $$CO_2$$, $$CH_4$$, $$N_2O$$ that trap infrared radiation. DDT does not participate in this mechanism, so Option A is incorrect.

Option B: Fertilizers supply essential nutrients (N, P, K, etc.) to plants. DDT is not used for plant nutrition, so Option B is incorrect.

Option C: A biodegradable pollutant can be decomposed by natural biological processes. DDT is resistant to such decomposition, so Option C is incorrect.

Option D: A non-biodegradable pollutant persists in the environment for long periods and accumulates in living organisms. DDT fits this definition, so Option D is correct.

Therefore, the correct answer is:
Option D which is: Non-biodegradable pollutant