Consider the following statements : Statement I : Some rare earth elements are used in the manufacture of flat television screens and computer monitors. Statement II : Some rare earth elements have phosphorescent properties. Which one of the following is correct in respect of the above statements?
- (a) Both Statement I and Statement II are correct and Statement II explains Statement I ✓ UPSC's answer
- (b) Both Statement I and Statement II are correct but Statement II does not explain Statement I
- (c) Statement I is correct but Statement II is not correct
- (d) Statement I is not correct but Statement II is correct
Why the answer is (a)
• Statement I is correct: rare earth elements such as europium, terbium and yttrium are used in the phosphor coatings of flat-panel television screens, computer monitors and LED backlights, giving the red, green and blue colours.
• Statement II is correct: several rare earths have luminescent (phosphorescent/fluorescent) properties — their electrons emit light of sharp, characteristic wavelengths when excited.
• It is precisely this luminescence that makes them useful in display phosphors, so Statement II explains Statement I.
• The same property is exploited in energy-saving lamps, lasers and anti-counterfeit inks.
• Hence option (a).
Why the other options are wrong
- (b) Both Statement I and Statement II are correct but Statement II does not explain Statement…
- The phosphorescent property is exactly why rare earths are used in screens, so II does explain I.
- (c) Statement I is correct but Statement II is not correct
- Statement II is also correct: rare earths are luminescent.
- (d) Statement I is not correct but Statement II is correct
- Statement I is also correct: rare earths are used in display phosphors.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2025, held on 25 May 2025. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.