2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/84260``Transition frequencies'' of a system containing an arbitrary number of bubbles levitated in a liquid are discussed. Using a linear coupled-oscillator model, it is shown theoretically that when the system contains $N$ bubbles of different sizes, each bubble has $2N - 1$ (or less) transition frequencies which make the phase difference between an external sound and a bubble's pulsation $π/ 2$. Furthermore, we discuss a discrepancy appearing between the present result regarding the transition frequencies and existing ones for the resonance frequencies in a two-bubble case, and show that the transition frequency, defined as above, and the resonance frequency have a different physical meaning when $N \ge 2$, while they are consistent for $N = 1$.5 pages, Revtex; "Eigenfrequency" replaced with "transition frequency", a numerical example added, and references removedFluid DynamicsAtmospheric and Oceanic Physicstext