📘 IAS Prelims 2025 — GS-I | Q.81 | Classroom Explanation
(Science & Technology | Materials & Electronics)

---

📌 Question

Q.81)
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
(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

---

✅ Correct Answer: (a)

---

🧑‍🏫 Classroom Explanation

This is a classic “Reason explains Assertion” type UPSC question, testing conceptual linkage rather than isolated facts.

---

🔬 Understanding Rare Earth Elements (REEs)

Rare Earth Elements (REEs) include 17 metallic elements:

• 15 Lanthanides
• Plus Scandium and Yttrium

They are critical for modern electronics due to their:

• ✨ Luminescent properties
• 🧲 Magnetic strength
• ⚡ High electrical and optical efficiency

---

🔍 Statement-wise Analysis

🔹 Statement I — Correct ✅

Certain REEs are essential for display technologies, especially:

• Europium (Eu) → Red phosphor
• Terbium (Tb) → Green phosphor
• Yttrium (Y) → Host material for phosphors

📺 Used in:

• Flat-screen TVs (LED, LCD)
• Computer monitors
• Smartphones and tablets

These elements enable sharp resolution and accurate colour reproduction.

---

🔹 Statement II — Correct ✅ and Explains Statement I

• Many REEs exhibit phosphorescence / luminescence
• They emit visible light when excited by:
  • Electron beams (older CRTs)
  • Electric current or UV light (modern displays)

🎨 This property is the exact reason they are used in:

• Colour pixels
• Backlighting systems
• High-efficiency display panels

📌 Thus, Statement II directly explains Statement I.

---

🧠 UPSC Memory Hook (Prelims Gold)

“Eu–Tb–Y glow = colour flow.”
(REE phosphors → colourful screens)

---

📍 GS Mapping

Advanced Materials | Electronics | Strategic Minerals

GS Paper III

Science & Technology

---