CN 0 \(-\mathrm{CH}_{2} \mathrm{CH}\) - repeating unit is made from which of the following monomer? (a) \(\mathr… # Polyacrylonitrile, characterized by the: N#CN 0 \)-\mathrm{CH}_{2} \mathrm{CH}\( - repeating unit is made from which of the following monomer? (a) \)\mathrm{CH}_{2}=\mathrm{CHCN}\( (b) \)\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CN}\( (c) \)\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\( (d) \)\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCN}$

Understanding the origin of polymers begins with identifying the monomers, the essential building blocks that combine chemically to form longer chains. As in the exercise where polyacrylonitrile's repeating unit is shown, we must trace back to the original, singular molecule that propagates the chain.

Monomers for polymers like polyacrylonitrile often have a double bond, which is key to the polymerization process. This double bond 'opens up' and links with other monomers to form the polymer chain. The given polymer contains a nitrile group - a carbon triple-bonded to nitrogen (CN) - which points us toward the correct monomer. By examining the structural features and functionalities of the options provided, we conclude that the monomer must have both the vinyl group (a molecular arrangement of -(CH2=CH)-) and the nitrile group at the appropriate position to maintain its structure in the newly formed polymer. Thus, in polyacrylonitrile, option (a) with the structure CH2=CHCN, correctly represents the starting molecule for the polymer chain.

The repeating unit is the most fundamental part of a polymer's structure because it defines its physical and chemical properties. This unit repeats itself over and over along the length of the polymer chain, giving rise to the macromolecule.

To identify the repeating unit of a polymer, look for the part of the structure that is bracketed and often indicated with 'n', such as in the case of polyacrylonitrile -(- CH2CH(CN))-n. After polymerization, the monomer's double bonds break and form single bonds with adjacent monomers, turning into this repeating structural unit. This transformation is a key concept in polymer chemistry and understanding how monomers react to create the diverse properties of synthetic polymers.

For students preparing for competitive exams like NEET, understanding polymer chemistry is vital. Questions often focus on knowledge of monomer-polymer relationships, types of polymerization reactions, and the structural analysis of polymers.

To tackle polymer-related questions in NEET, students must grasp the named reactions and mechanisms involved in polymer formation. Polyacrylonitrile polymerization, for instance, requires a clear understanding of addition polymerization, where monomers like acrylonitrile ( CH2=CHCN ) add on to each other without losing any atoms in the process.

Remember, mastering polymer chemistry for NEET significantly hinges on visualizing the polymerization process and being able to work backwards from a polymer to its monomer, just like reversing an engineered product to its blueprint. Such a conceptual approach aids in efficiently navigating chemistry sections in competitive exams like NEET.