Historic antiknock dosing: Approximately how much tetraethyl lead (TEL) was traditionally added to motor gasoline to raise octane, expressed in cubic centimetres per US gallon?

Introduction:
Before the widespread phase-out of leaded fuels, small doses of tetraethyl lead (TEL) dramatically improved gasoline octane rating. Knowing the correct order of magnitude prevents unit mistakes and highlights the potency of TEL as an antiknock agent.

Given Data / Assumptions:

• Dosing is stated per gallon of gasoline.
• Historic typical additions were in a few millilitres per gallon, not hundreds.

Concept / Approach:
TEL is effective at very low concentration. Typical historical additions were on the order of a few c.c. per gallon, commonly around 3 c.c per gallon for many commercial grades, with exact amounts depending on base fuel quality and desired octane uplift.

Step-by-Step Solution:

Verification / Alternative check:
Historic specs and training texts cite TEL treat rates in the low single-digit millilitres per gallon range.

Why Other Options Are Wrong:

• 300 / 1000 / 3000: Unrealistic and unsafe; would grossly over-treat fuel.
• 0.3: Too low for typical legacy uplift targets.

Common Pitfalls:
Confusing millilitres (c.c.) with microlitres or misplacing decimals.

Final Answer:
3