In the processing of synthetic plastics, why are plasticizers incorporated into the polymer formulation? Select the most comprehensive reason.

Introduction / Context:
Plasticizers are low-molecular-weight additives that modify polymer mobility, glass transition temperature, and processability. Understanding their role is central to tailoring properties of PVC, nitrile rubbers, and many other plastics used in cables, flooring, and flexible containers.

Given Data / Assumptions:

• Base resin is relatively rigid or has a high glass transition temperature.
• Additive is compatible and dispersible within the polymer matrix.
• Application demands flexibility, ease of shaping, or special performance attributes.

Concept / Approach:
Plasticizers increase free volume and chain mobility, lowering the glass transition temperature (Tg). This yields softer, more flexible materials, reduces melt viscosity during processing, and can introduce properties like low-temperature flexibility or improved impact resistance when properly formulated.

Step-by-Step Solution:

Verification / Alternative check:
Empirical PVC data show significant Tg depression with phthalates, adipates, or citrate plasticizers, correlating with measured flexibility and processability improvements.

Why Other Options Are Wrong:

• Single-benefit choices (a), (b), or (c) are incomplete; plasticizers commonly deliver all listed effects when compatibilized.

Common Pitfalls:
Ignoring compatibility limits and migration; not all plasticizers suit every polymer, and excessive levels can exude or reduce mechanical strength.

Final Answer:
all (a), (b) and (c)