Clay treatment (adsorptive finishing) is used on various petroleum streams. Identify the effect it is chiefly known for among the following: decolorising and stabilising cracked gasoline, desulphurising straight-run gasoline/kerosene, adsorbing arsenic from reforming feeds, or “all of the above.”

Introduction / Context:
Clay (activated clay/earth) finishing is an adsorption process applied to selected petroleum fractions to remove color bodies, gums, and polar contaminants. It is especially associated with improving appearance and stability of cracked gasolines and certain distillates.

Given Data / Assumptions:

• Media: acid-treated/activated clays with high surface area.
• Streams: cracked gasoline, sometimes kerosene/light distillates.
• Targets: color bodies, olefinic polymers, trace oxygenates, and polar species.

Concept / Approach:
Clay treatment is primarily an adsorptive polish. It is not a chemical desulphurization process; sulphur reduction to specification typically requires hydrotreating or sweetening. While certain metals can be adsorbed by specialized guard beds (e.g., alumina or proprietary sorbents), arsenic removal for reforming is not a standard role for clay finishing in this context.

Step-by-Step Solution:

Verification / Alternative check:
Finishing sections in refinery processing texts list clay towers for color/gum reduction on cracked naphthas and kerosenes, not for deep sulphur removal or arsenic trapping for reformers.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming any adsorbent removes all contaminants; adsorption is selective and often limited for sulphur/metals versus hydrogenation routes.

Final Answer:
Decolorises and stabilises cracked gasoline