The relationship between exhaust molar mass and specific impulse is a fundamental principle of rocket propulsion derived directly from the rocket equation and thermodynamics, making it common knowledge that requires no citation.
The claim states that lower molar mass rocket exhaust products yield higher specific impulse. This is a direct physical and thermodynamic consequence of the ideal gas law and rocket propulsion equations (specifically, specific impulse is inversely proportional to the square root of the mean molecular weight of the exhaust gases). None of the retrieved papers specifically test or focus on proving this fundamental relationship; rather, it is a basic textbook principle of rocketry and thermodynamics. Therefore, the claim is classified as common knowledge requiring no citation.