Step 1: Understanding the Concept:
Polymers are classified by their mode of polymerization. Addition polymers usually proceed via a chain-growth mechanism, while condensation polymers usually proceed via a step-growth mechanism.
Step 2: Detailed Explanation:
1. Polystyrene: It is formed by the addition polymerization of styrene monomers. Addition polymerization involves the formation of reactive intermediates (like free radicals) that rapidly add monomers to a growing chain. This is called a chain-growth polymerization.
2. Dacron (Terylene): It is a polyester formed by the condensation reaction between ethylene glycol and terephthalic acid with the elimination of water molecules. Condensation polymerization involves the reaction between functional groups, and any two species can react to form a dimer, then a trimer, etc. This is called step-growth polymerization.
Step 3: Final Answer:
Polystyrene is chain growth, and Dacron is step growth. Option B is correct.