Nitrile rubber (NBR): Identify the correct pair of monomers used to produce this oil-resistant elastomer by copolymerization.

Introduction / Context:
Nitrile rubber (NBR) is valued for its resistance to oils, fuels, and many chemicals. It is ubiquitous in seals, O-rings, fuel hoses, gloves, and gasketing. The question assesses knowledge of the monomer composition underlying these performance traits.

Given Data / Assumptions:

• NBR is a copolymer rather than a homopolymer.
• Candidate monomers include common vinyl and diene species.
• Oil resistance correlates with polar nitrile content in the copolymer.

Concept / Approach:
NBR results from emulsion or solution copolymerization of acrylonitrile (ACN) with 1,3-butadiene. The ACN content (typically 18–50%) tunes polarity and oil resistance: more ACN improves fuel/oil resistance but reduces low-temperature flexibility. The butadiene segments provide elastomeric behavior and processability.

Step-by-Step Solution:

Verification / Alternative check:
Specifications for NBR (e.g., ASTM designations) list ACN content to classify grades, confirming the monomer set.

Why Other Options Are Wrong:

• Acrylonitrile & styrene: Leads to SAN, a rigid copolymer (used in ABS blends) not an oil-resistant elastomer.
• Isobutylene & isoprene: Forms butyl rubber (IIR), a different elastomer with low gas permeability, not NBR.
• None of these: Incorrect because option (a) is correct.

Common Pitfalls:
Assuming all nitrile-named materials are homopolymers of acrylonitrile; NBR is a copolymer with critical composition balance.

Final Answer:
acrylonitrile & butadiene