Key requirement of a good I.C. engine combustion chamber: choose the best criterion. Select the most appropriate characteristic of a well-designed combustion chamber.

Concept/Approach
An effective combustion chamber promotes rapid, stable combustion (adequate turbulence and mixture motion), good volumetric efficiency, and supports higher compression ratios—leading to high efficiency and power density.

Why others are wrong
“Minimum turbulence” harms combustion speed; “low compression ratio” and “low volumetric efficiency” reduce performance.

Final Answer
High thermal efficiency and power output.