Select the correct statements about lanthanoids:
(A). Lanthanoids are good conductors of heat and electricity
(B). Ln oxides are used as phosphors in TV screens
(C). Their Melting points range between 2100 to 2300 K
(D). It is used for the production of alloy steels
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (D) only
The lanthanoids (Ce to Lu) are silvery-white soft metals with typical metallic properties. Their uses come mainly from alloys (mischmetall, alloy steels), mixed oxides (catalysts) and individual oxides (phosphors).
(A) Lanthanoids are good conductors of heat and electricity — Correct. They have a typical metallic structure, with delocalised electrons that carry heat and charge.
(B) Ln oxides are used as phosphors in TV screens — Correct. Some individual lanthanoid oxides glow when struck by electrons, so they are used as phosphors in television screens and similar fluorescing surfaces.
(C) Their Melting points range between 2100 to 2300 K — Incorrect. Their melting points lie between about 1000 and 1200 K; samarium, the highest, melts at 1623 K. No lanthanoid melts at 2100–2300 K.
(D) It is used for the production of alloy steels — Correct. The best single use of the lanthanoids is in alloy steels for plates and pipes. Mischmetall (a lanthanoid metal about 95% with iron about 5%) is used in Mg-based alloys for bullets, shells and lighter flints.
Shortcut: Judging (C) alone settles the question: it is false, and Option (1) is the only option that leaves it out.
NCERT (2026-27 edition):
Physical Properties – “All the lanthanoids are silvery white soft metals and tarnish rapidly in air. The hardness increases with increasing atomic number, samarium being steel hard. Their melting points range between 1000 to 1200 K but samarium melts at 1623 K. They have typical metallic structure and are good conductors of heat and electricity.”
Uses of Lanthanoids – “The best single use of the lanthanoids is for the production of alloy steels for plates and pipes. A well known alloy is mischmetall which consists of a lanthanoid metal (~ 95%) and iron (~ 5%) and traces of S, C, Ca and Al. A good deal of mischmetall is used in Mg-based alloy to produce bullets, shell and lighter flint. Mixed oxides of lanthanoids are employed as catalysts in petroleum cracking. Some individual Ln oxides are used as phosphors in television screens and similar fluorescing surfaces.”