The soft silvery metalic element which ionizes easily when heated or exposed to light and is present in atomic clocks is –

A. Cerium
B. Cesium
C. Calcium
D. Californium
Answer» B. Cesium
Explanation: 1967, based on Einstein defining the speed of light as the most constant dimension in the universe, the International System of Units isolated two specific wave counts from an emission spectrum of caesium133 to codefine the second and the meter. Since then, caesium has been widely used in highly accurate atomic clocks. Among alkali metals, cesium has lowest ionization energy and hence it can show photoelectric effect to the maximum extent.
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