2025 GS Paper I, all questions

UPSC Prelims 2025 · GS Paper I

Question 81: Science and Technology

Consider the following statements :

  1. Statement ISome rare earth elements are used in the manufacture of flat television screens and computer monitors.
  2. Statement IISome rare earth elements have phosphorescent properties.

Which one of the following is correct in respect of the above statements?

aBoth Statement I and Statement II are correct and Statement II explains Statement I
bBoth Statement I and Statement II are correct but Statement II does not explain Statement I
cStatement I is correct but Statement II is not correct
dStatement I is not correct but Statement II is correct

AnswerThe answer is (a).

Several rare earth elements, such as europium, terbium and yttrium, are used to make the phosphors that give colour in flat television screens and computer monitors, so Statement I is correct. These elements have luminescent, phosphorescent properties: they emit visible light when excited, which is exactly what is needed for a display to produce red, green and blue. So Statement II is correct and it explains Statement I. Remember: rare earth phosphors colour the screen.

  • I. Rare earth phosphors are used in flat screens and monitors.
  • II. Some rare earths emit light when excited; this explains Statement I.

How you could have got this

If you were sure Statement I is correct, (d) goes. Then judge the second statement; if it is correct too, decide whether it explains the first.

What you needed to know: Rare earth phosphors are used in flat screens and monitors.

This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.

Which options go is worked out from UPSC’s key and the options, not by a model.

Why each option is right or wrong
  • (a) Right: both are correct and the light-emitting property is why rare earths are used in screens.
  • (b) Wrong: the phosphorescent property is the reason for their use in screens.
  • (c) Wrong: Statement II is also correct.
  • (d) Wrong: Statement I is also correct.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2025, General Studies Paper I, Series A. The paper on upsc.gov.in.