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?
Show answer
Answer: A. Statement I is correct: rare earths such as europium, terbium and yttrium are used in screens and monitors. Statement II is correct: these elements are phosphorescent, giving off coloured light (red, green, blue) when excited. That glowing property is exactly why they are used in displays, so Statement II explains Statement I.
Watch for: Both statements are true; the test is whether the light-emitting property is the reason for use in screens (it is).
Why the other options are wrong
- B. Statement II does explain Statement I, since phosphor property is the reason for their use in screens.
- C. Statement II is also correct.
- D. Statement I is also correct.
Source to check: Ministry of Mines / IREL (India) Rare Earths Ltd material on rare earth uses; USGS rare earth fact sheets.
Answer from the official UPSC key. Written and fact-checked by AI against the official key. Spotted a mistake? Report it.