Paraffin waxes are commercially graded using a key specification relevant to product performance and end use. Select the standard parameter used for grading: specific gravity, melting point, viscosity, or penetration number.

Introduction / Context:
Paraffin waxes find use in packaging, candles, coatings, and cosmetics. Grading ensures the right wax is selected for thermal and mechanical performance in the application environment.

Given Data / Assumptions:

• End-use demands focus on softening and thermal behavior.
• Multiple properties can be measured, but one is primary for grading.
• Industry naming often references this key property.

Concept / Approach:
Melting point (or congealing point) is the primary grading metric for paraffin waxes because it directly dictates handling temperatures, set time, and stability in service. While oil content and needle penetration are specified for quality control, the commercial “grade” usually centers on melting point (e.g., 58–60°C wax).

Step-by-Step Solution:

Verification / Alternative check:
Supplier datasheets and standards commonly list melting range as the headline grade with auxiliary specs for oil content and penetration.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing general QC parameters with the commercial grade label.

Final Answer:
Melting point