Indian Forest Service (Mains), Chemistry optional · 2025 · Paper I

Q8(c)(ii). Blue colour in liquid ammonia

5 marks
Topic: Non-aqueous solvents
Question only

Question

Why do dilute solutions of different alkali metals in liquid ammonia have the same blue colour?

Model answer

The free solution for 2025 answers questions 1, 2, 3, 5 and 6, the ones picked in its time plan. Question 8 is answered in full in the IFoS Chemistry Paper I, 2021 to 2025 book, with every part of every paper.

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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

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Topic notes: non-aqueous solvents: liquid ammonia, HF, sulfuric acid, SO₂, BrF₃ and superacids, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversblue colour liquid ammoniasolvated electronammoniated electronalkali metal solutions

All parts of Question 8

8(a)(i) Alkyne–dicobalt bonding10 marks
8(a)(ii) Alkene insertion into metal bonds5 marks
8(b)(i) Lanthanide separation by valence change5 marks
8(b)(ii) Similarity of second and third transition series10 marks
8(c)(i) Conductance of metal–ammonia solutions5 marks
8(c)(ii) Blue colour in liquid ammonia5 marks