Refining processes and thermal severity: Identify which of the following common refinery processes does not involve hydrocarbon chain cracking under its core mechanism.

Introduction / Context:
Many refinery conversion processes rely on breaking heavy hydrocarbon chains into lighter molecules—thermal or catalytic cracking. Understanding which processes intrinsically crack vs. those that do not is a core refinery fundamentals skill.

Given Data / Assumptions:

• Processes listed: coking, visbreaking, and pyrolysis.
• Thermal severity ranges from mild (visbreaking) to severe (coking, steam cracking).
• We assess the core mechanism, not ancillary steps.

Concept / Approach:
Coking, visbreaking, and pyrolysis are all thermal cracking processes. Therefore, none of them qualifies as "does not employ cracking."

Step-by-Step Solution:

Verification / Alternative check:
Standard process flow diagrams and unit operation descriptions confirm cracking in all three listed processes.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing "visbreaking" as purely viscosity adjustment without cracking; in fact, it achieves viscosity reduction via mild cracking.

Final Answer:
None of these (all involve cracking)