Q. The soft silvery metalic element which ionizes easily when heated or exposed to light and is present in atomic clocks is :
Answer: Cesium
Notes: In 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 caesium-133 to co-define the second and the meter. Since then, caesium has been widely used in highly accurate atomic clocks. Among alkali metals, cesium melting point 38.4°C has lowest ionization energy Hence, it can show photoelectric effect to the maximum extent.