Q3(a). Ionic distances and radius-ratio predictions
(i) The density of NaCl is 2.17 g cm⁻³. Calculate the interionic distance. (F. wt. of NaCl = 58.45.) (ii) The ionic radii of Rb⁺, Br⁻ and I⁻ ions are 1.47 Å, 1.95 Å and 2.16 Å respectively. Predict the most probable type of geometry exhibited by RbBr and RbI on the basis of radius ratio rule. (5+5 marks)
Model answer
The free solution for 2023 answers questions 1, 2, 4, 5 and 6, the ones picked in its time plan. Question 3 is answered in full in the IFoS Chemistry Paper I, 2021 to 2025 book, with every part of every paper.
Part of VKC Basic
Read the key points and the full model answer with VKC Basic
VKC Basic (₹999 for 6 months) opens every solved answer, the notes, the handbook and the daily answer archive. Every Mains test series includes it.
UPSC Indian Forest Service (Main) Chemistry Paper I: Model Answers 2021 to 2025
- All eight questions of each paper, with the question printed above its answer
- Physical chemistry numericals worked with units; inorganic structures drawn
- Topic-wise weightage and a topic-wise index
Coversradius ratio ruleinterionic distanceNaCl densityRbBrRbIcoordination geometry
All parts of Question 3
- 3(a) Ionic distances and radius-ratio predictions10 marks
- 3(b) Avogadro constant from diffraction10 marks
- 3(c) Ideal and van der Waals pressures10 marks
- 3(d) Pressure as a state function10 marks