In petroleum product testing, the smoke volatility index (SVI) is defined numerically as the smoke point (in mm) plus a factor multiplied by the percentage distilled at 204 °C. Which factor correctly completes this industry relation?

Introduction:
The smoke volatility index (SVI) is a quick empirical indicator used for kerosene-range fuels to balance their smoke-forming tendency (linked to aromatics/heavies) against volatility (linked to front-end distillate recovery). A correct understanding of the SVI expression helps technicians compare jet/kerosene product quality in the lab without running advanced instruments.

Given Data / Assumptions:

• SVI is computed from the smoke point (mm) and a fraction of the volume percent distilled at 204 °C.
• We are selecting the correct multiplicative factor for the 204 °C distillation percent.
• Units: smoke point in mm; distilled percentage in vol %.

Concept / Approach:
By definition in common refinery lab practice, the smoke volatility index is calculated as:
SVI = smoke point (mm) + 0.42 * (% distilled at 204 °C)Higher SVI indicates a more favorable combination of lower smoke tendency and adequate volatility for clean combustion, particularly relevant for aviation/kerosene grades.

Step-by-Step Solution:
1) Identify the required empirical relation for SVI.2) Recall the standard coefficient applied to the 204 °C recovery: 0.42.3) Choose the option that matches SVI = smoke point + 0.42 * (204 °C recovery).

Verification / Alternative check:
Refinery QA guides and petroleum testing manuals cite this empirical correlation for kerosene-type fuels to complement separate smoke point and volatility assessments.

Why Other Options Are Wrong:
5 mm, 10 mm: Fixed offsets are not used in the definition.0.84 or 0.24: Incorrect coefficients; would distort comparative SVI values.

Common Pitfalls:
Mixing up SVI with pure smoke point or assuming a fixed additive constant instead of the correct proportional term tied to 204 °C distillation percentage.

Final Answer:
0.42 * (% distilled at 204 °C)