Visbreaking is applied to heavy fuel oils/residua primarily to make handling and use easier. Identify the key property it targets for reduction—considering pour point, viscosity, and pumping pressure drop.

Introduction / Context:
Visbreaking is a mild thermal cracking process applied to heavy residues to make them more marketable and easier to handle. It achieves limited conversion without excessive gas/coke formation and is common ahead of blending bunker fuels or selling fuel oil grades.

Given Data / Assumptions:

• Feed: atmospheric or vacuum residue/heavy fuel oil.
• Objective: improve handling and product value.
• Measured properties: viscosity, pour point, pumpability.

Concept / Approach:
The defining specification improved by visbreaking is viscosity. By cracking large molecules to smaller ones, viscosity falls markedly, enabling compliance with viscosity-grade limits. While pumpability and sometimes pour point can benefit indirectly, these are secondary consequences of viscosity reduction and blending strategies.

Step-by-Step Solution:

Verification / Alternative check:
Product specifications for fuel oils heavily emphasize viscosity grades; visbroken residue is commonly blended to meet them.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming every property that improves indirectly is a primary process target; focus on the specification that drives the operation design.

Final Answer:
Viscosity