Question

Which of the following statement(s) is/are correct?

• A. Starch is composed of repeating $\alpha$-D-glucose units.
• B. Nylon-6 is an addition polymer whereas nylon-6,6 is a condensation polymer.
• C. Isoprene is the monomer unit of natural rubber.
• D. Bakelite is obtained from reaction between phenol and acetaldehyde.

Hint:

Keep a handy summary of polymer classifications:
- Starch $\rightarrow$ polymer of $\alpha$-D-glucose.
- Cellulose $\rightarrow$ polymer of $\beta$-D-glucose.
- Natural rubber $\rightarrow$ cis-1,4-polyisoprene.
- Bakelite $\rightarrow$ Phenol + Formaldehyde ($\text{HCHO}$).

Answer 1

The Correct Option is A, C

Step 1: Understanding the Concept:
This question tests general knowledge of polymers and natural polysaccharides. We need to identify the correct monomers and polymerization types.
Step 2: Detailed Explanation:
- Statement (A): Correct. Starch is a polysaccharide made of $\alpha$-D-glucose monomers. It consists of two components: amylose (linear $\alpha$-1,4 linkages) and amylopectin (branched $\alpha$-1,4 and $\alpha$-1,6 linkages).
- Statement (B): Incorrect. While Nylon-6 is made from caprolactam via a ring-opening mechanism (which looks like addition), it is generally classified as a condensation polymer (step-growth) because the backbone contains the amide linkage characteristic of condensation. Both Nylon-6 and Nylon-6,6 are condensation polymers.
- Statement (C): Correct. Natural rubber is cis-1,4-polyisoprene. Its monomer unit is 2-methylbuta-1,3-diene, commonly called isoprene.
- Statement (D): Incorrect. Bakelite is a thermosetting phenol-formaldehyde resin. It is obtained from the condensation reaction of phenol with formaldehyde ($HCHO$), not acetaldehyde ($CH_3CHO$).
Step 3: Final Answer:
The correct statements are (A) and (C).