Which of the following statements are true?
(A) Noble gases have low m.p. or b.p. due to weak dispersion forces
(B) All noble gases have completely filled \(ns^2np^6\) electronic configuration
(C) \(XeF_2\) and \(XeF_6\) are colourless crystalline solid
(D) \(XeO_3\) has pyramidal geometry
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A), (C), (D) only
The noble gases are monatomic with stable closed-shell configurations; only xenon forms well-known compounds (fluorides and oxides), whose shapes follow from VSEPR theory.
(A) Noble gases have low M.P. or B.P. due to weak dispersion forces — Correct. The atoms are held only by weak London (dispersion) forces, so melting and boiling points are low.
(B) All noble gases have completely filled ns2np6 electronic configuration — Incorrect. Helium is 1s2; it has no p electrons. Only Ne to Rn are ns2np6.
(C) \( \ce{XeF2} \) and \( \ce{XeF6} \) are colourless crystalline solid — Correct. \( \ce{XeF2} \), \( \ce{XeF4} \) and \( \ce{XeF6} \) are colourless crystalline solids that sublime readily at 298 K.
(D) \( \ce{XeO3} \) has pyramidal geometry — Correct. Xe (8 valence electrons) uses 6 in three Xe=O bonds and keeps one lone pair: 3 bonding positions + 1 lone pair give a pyramidal shape.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.