Which one of the following correctly describes the principle of the working of an atomic clock?

The working principle of an atomic clock is based on the resonant frequency of specific atoms, most commonly cesium-133 or rubidium [1]. Unlike quartz clocks that rely on the mechanical vibration of a crystal, atomic clocks utilize the ground-state hyperfine transition of atoms [2]. In a cesium-beam frequency standard, the SI second is defined as 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the cesium-133 atom. The clock functions by adjusting and maintaining the frequency of an electronic oscillator to match this stable reference atomic transition frequency. While other atoms like rubidium or hydrogen can be used, the core mechanism remains the interrogation of atoms at their specific resonating frequencies to provide a spectroscopic signal that stabilizes the timekeeping loop.

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 8: Measurement of Time and Motion > THINK LIKE A SCIENTIST! > p. 111
2. [2] https://tf.nist.gov/general/pdf/1402.pdf