Final answer:
The threshold frequency for cesium is not provided in the information given. It would require knowledge of cesium's work function to calculate it using the photoelectric effect equation.
Step-by-step explanation:
The concept of threshold frequency is fundamental in the study of photoelectric effect in Physics. However, the information provided does not specify the threshold frequency for cesium (Cs). To calculate the threshold frequency (ν0) for any element, including cesium, we would need to use the photoelectric effect equation, E= hν - Φ, where E is the energy of the emitted electron, h is Planck's constant, ν is the frequency of the incoming photon, and Φ is the work function of the metal. Since the work function is unique to each element and not given in the information for cesium, we cannot calculate the threshold frequency directly without this data. Generally, the threshold frequency is the minimum frequency of light needed to eject an electron from a metal surface. The given facts about cesium's use in time-keeping and the potential for future atomic clocks do not relate to the question about threshold frequency.