The correct answer is option 3, Polythene. This is because polythene is not a condensation polymer. Condensation polymers are formed through a condensation reaction, in which two monomers react and eliminate a small molecule like water or alcohol. This reaction occurs repeatedly to form a long chain of repeating units.

Option 1, Nylon, is a condensation polymer. It is formed through the reaction between diacid and a diamine, which eliminates water as a byproduct. Nylon is commonly used in textiles and engineering materials.

Option 2, DNA (Deoxyribonucleic acid), is also a condensation polymer. DNA is formed by the condensation reaction between nucleotides, which eliminates water. It is the genetic material that carries the hereditary information in all living organisms.

Option 4, Bakelite, is a condensation polymer as well. It is formed by the condensation reaction between phenol and formaldehyde, resulting in the elimination of water. Bakelite is a thermosetting plastic and was one of the first synthetic plastics invented.

Therefore, out of the given options, polythene (option 3) is not a condensation polymer.