Polymers practice · Mixed difficulty

Option B (SBR) is correct because SBR (styrene-butadiene rubber) is a copolymer, not a homopolymer, as it is made from two different monomers.

Option A (Bakelite) is correct because Bakelite is formed through a step-growth polymerization process involving condensation reactions.

Option A is correct because low-density polythene (LDPE) is produced through free radical polymerization at high pressure and temperature.

Option D (All of the above) is correct because thermosets are cross-linked polymers that do not melt or soften upon heating, and their cross-linking is usually developed during moulding.

Option D is correct because DNA is a naturally occurring polymer composed of nucleotide monomers.

Option B (fibres) is correct because fibres have the strongest intermolecular forces due to their highly ordered structure and strong hydrogen bonding.

Option C ($B < C < A$) is correct because the intermolecular forces increase in the order: Buna-S (weakest), Polythene, and Nylon 6,6 (strongest).

Option D (Glycogen) is correct because glycogen is the storage form of glucose in animals.

Option A (Intermolecule H-bonding) is correct because Nylons, polyesters, and cotton all exhibit intermolecular hydrogen bonding, contributing to their strength.

Option C ($\mathrm{C}{\mathrm{H}_2} = \mathrm{CH}{\mathrm{C}_6}{\mathrm{H}_5}$) is correct because the presence of the phenyl group stabilizes the propagating radical, facilitating chain growth polymerization.

Option B (Atactic product) is correct because catalytic hydrogenation of natural rubber results in an atactic product due to the random addition of hydrogen atoms.

Option D (Thermosetting) is correct because Bakelite is a thermosetting polymer, meaning it undergoes irreversible hardening upon heating.

Option A (Both A and R are correct, and R is the correct explanation of A) is correct because natural rubber's elastomeric properties arise from the weak van der Waals forces between its polymer chains.

Option D (Nylon 66) is correct because Nylon 66 is formed through a step-growth polymerization mechanism.

Option B is correct because SBR (Styrene-Butadiene Rubber) is a synthetic rubber, not natural rubber.

Option C (Amino acids) is correct because proteins are polymers made up of amino acid monomers linked together by peptide bonds.

Option D is correct because Nylon-66 contains nitrogen atoms in its amide linkages.

Option C (Thiokol rubber) is correct because Thiokol rubber is a polysulfide rubber, not a polydiene.

Option A (Buna-S) is correct because Buna-S is formed by the addition polymerization of butadiene and styrene.

Option C is correct because Nylon-66 is a polyamide, formed by the condensation polymerization of a diamine and a dicarboxylic acid.

Option C (Perlon) is correct because Perlon (Nylon-6) is a condensation homopolymer formed from caprolactam.

Option B (> 1) is correct because the polydispersity index (PDI) is the ratio of mass average molecular mass to number average molecular mass, and for polymers, this value is always greater than 1.

Option C ($>1$) is correct because the polydispersity index (PDI) is the ratio of mass average molar mass to number average molar mass, and for polymers, this value is always greater than 1.

Option A (1,3-butadiene) is correct because Buna rubber is a polymer primarily made from 1,3-butadiene.

Option C (Phenol) is correct because phenol is a common raw material in the synthesis of salicylic acid, aspirin, nylon, plastics (like Bakelite), and picric acid.

Option B (Neoprene) is correct because it is an addition polymer, while Dacron, Melamine, and Glyptal are condensation polymers.

Option D (All of these) is correct because crystallinity, melting point, and molecular weight all contribute to the tensile strength of a polymer.

Option A (Cis - polyisoprene) is correct because cis-polyisoprene (natural rubber) is a natural polymer, not a semisynthetic one.

Option A (Both assertion and reason are correct statements, and reason is the correct explanation of the assertion) is correct because natural rubber's elasticity is due to the coiled structure of cis-polyisoprene held together by weak van der Waals forces.

Option D is correct because cellulose acetate is less flammable than cellulose nitrate and is used in photographic films.