Identify the monomers used to obtain the polymer Buna N in the presence of a peroxide catalyst.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → B and C only
Buna-N is a synthetic rubber made by addition copolymerisation of two monomers, 1,3-butadiene and acrylonitrile, in the presence of a peroxide catalyst (which supplies the free radicals that start the chain):
\( \ce{nCH2=CH-CH=CH2 + nCH2=CH-CN} \xrightarrow{\text{peroxide}} \left[ \ce{-CH2-CH=CH-CH2-CH2-CH(CN)-} \right]_{n} \)
The polar –CN groups make Buna-N resistant to petrol, lubricating oil and organic solvents; it is used for oil seals and tank linings.
(A) \( \ce{CH2=CHCl} \), vinyl chloride — Incorrect. It is the monomer of PVC.
(B) \( \ce{CH2=CH-CN} \), acrylonitrile — Correct. It supplies the “N” of Buna-N.
(C) \( \ce{CH2=CH-CH=CH2} \), 1,3-butadiene — Correct. It supplies the “Bu”; “na” stands for sodium, once used as the catalyst.
(D) \( \ce{CH2=C(Cl)-CH=CH2} \), chloroprene (2-chloro-1,3-butadiene) — Incorrect. It polymerises alone to neoprene.
(E) \( \ce{C6H5-CH=CH2} \), styrene — Incorrect. With 1,3-butadiene it gives Buna-S.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Buna-N
