The correct answer is (c). The clock is based on a single ytterbium ion, which is an atom of the element ytterbium with one electron removed. The ion is trapped in a vacuum chamber and subjected to a laser beam that causes it to oscillate at a very precise frequency. This frequency is used to keep time, and the clock is so precise that it can lose or gain only one second in 300 million years.
The other options are incorrect because they are not the elements used in the clock. Mercury is a metal that is used in thermometers and other devices. Titanium is a metal that is used in aircraft and other applications. Platinum is a metal that is used in jewelry and other applications. Aluminum is a metal that is used in construction and other applications.
The ytterbium ion was chosen for the clock because it has a very stable energy level. This means that it can be used to create a very precise frequency. The laser beam is used to excite the ion to a higher energy level, and then the ion decays back to its ground state. This decay process releases a photon of light, and the frequency of this light is used to keep time.
The clock is so precise that it can be used to measure the Earth’s rotation. It can also be used to study the behavior of subatomic particles. The clock is a major breakthrough in the field of timekeeping, and it is expected to have a wide range of applications.