Exp) Option a is the correct answer.

Rare earth elements (REEs) are a group of 17 chemically similar elements, including the 15 lanthanides along with scandium and yttrium. These elements possess unique magnetic, luminescent, and electrochemical properties, making them essential in various high-tech applications, including electronics, renewable energy, and defense.

Statement I is correct. Rare earth elements such as europium, terbium, and yttrium are integral in the production of phosphors used in display technologies. These phosphors emit specific colours when excited by electrons, enabling the vivid displays in flat-screen televisions and computer monitors. For instance, europium is used for red phosphors, terbium for green, and yttrium serves as a host lattice for these phosphors.

Statement II is correct. Certain rare earth elements exhibit phosphorescence, a type of photoluminescence where materials emit light after being energized. Elements like europium and terbium are known for their phosphorescent properties, which are harnessed in various applications, including lighting and display technologies.

Statement II explains Statement I. The phosphorescent properties of rare earth elements are the reason they are used in manufacturing display screens. The ability of these elements to emit light upon excitation is fundamental to the functioning of phosphors in screens, thereby directly linking their phosphorescent nature to their application in display technologies.

Source: https://indianexpress.com/article/upsc-current-affairs/upsc-essentials/knowledge-nugget-rare-earth-elements-national-critical-minerals-mission-upsc-prelims-2025-9866124/ ; https://www.energy.gov/sites/prod/files/2020/02/f71/Rare%20Earth%20Elements%20Infographic.pdf