Main Group Chemistry – Chemistry Optional PYQs (2000–2026)

Here are all 57 Main Group Chemistry questions asked in UPSC Chemistry Optional Paper I from 2000 to 2026, arranged under the 5 topics of the official syllabus. Within each topic the latest questions come first.

Each question ends with a code such as [2024/15m/3b] – the year, the marks, the word limit (where UPSC set one) and the question number in the paper.

Topic-wise weightage graph of Main Group Chemistry, Chemistry Optional Paper I, 2013–2026 vs 2022–2026 — Topic-wise weightage of Main Group Chemistry (Paper I) – share of marks, 2013–2026 (white) vs 2022–2026 (black).

14.1] Boranes and borazines

13 questions

What is inorganic benzene? Explain it with structure. [2026/5m/5i]
Describe the structure and bonding in diborane. [2026/10m/8b(i)]
Draw the structure of $B_{2} H_{6}$ . Explain the bonding in $B_{2} H_{6}$ on the basis of hybridization approach. [2024/10m/8b(ii)]
Complete the following reactions and draw the structure of the major product(s) formed: (i) $2 X e F_{6} + S i O_{2} \overset{50^{\circ} C}{\to}$ ____ (ii) $N H_{4} N O_{3} \overset{520 K}{\to}$ ____ + ____ (iii) $N_{2} O + N a N H_{2} \overset{470 K}{\to}$ ____ (iv) $2 B_{2} H_{6} + 6 N H_{3} \overset{180^{\circ} C}{\to}$ ____ + ____ (v) $6 S C l_{2} + 16 N H_{3} \to$ ____ + ____ + ____. [2023/10m/6a]
Predict the number of framework bonding electrons and the structure of the following boranes: (i) $B_{7} H_{7}^{2 -}$ (ii) $B_{11} H_{13}^{2 -}$ (iii) $B_{2} H_{7}^{-}$ [2023/10m/6e]
(i) How $X e F_{6}$ can be separated from a mixture of $X e F_{2}$ , $X e F_{4}$ and $X e F_{6}$ ? (ii) Write the products with explanation $B_{2} H_{6} + 2 N H_{3} \to ?$ $B_{2} H_{6} + 2 M e_{3} N \to ?$ [2022/10m/6d]
What is inorganic benzene? Write down its structural formula. [2020/5m/7b(i)]
What is inorganic benzene? How is it prepared? Compare and contrast the reactivities of inorganic benzene and benzene. [2019/10m/4c(ii)]
How diborane can be synthesized industrially? Draw the structure of diborane. Comment on the nature of boron-hydrogen bond present in it. [2018/10m/6d]
Discuss the structure and bonding in diborane. [2012/10m/3c(i)]
Which compound is called ‘inorganic benzene’ and why? [2012/12m/6e]
(i) Borazine is a close analogue of benzene. Explain on the basis of preparation, molecular structure and reactions of borazine. (ii) Discuss magnetic and spectral properties of lanthanides. [2011/20m/6b]
Identify the products A and B in the reaction given below:

[Figure: B-vinylborazine (borazine ring B3N3 with H on each N and on two B atoms, a vinyl group CH=CH2 on the third B) –Borazine, 125° C→ A –1000° C, NH3→ B] [2002/15m/7a]

14.2] Phosphazenes

7 questions

How does the bonding in cyclic phosphazene differ from that of benzene and borazine? [2021/10m/6a]
Define phosphazenes with formulae for ring and chain types. Write two examples of substitution reactions of cyclophosphazenes.

Values of fundamental physical constants (printed at the head of Section A of Paper I): Planck’s constant $h = 6.6262 \times 10^{- 34} J s$ ; mass of electron $m = 9.1091 \times 10^{- 31} k g$ ; charge on electron $e = 1.60210 \times 10^{- 19} C$ ; velocity of light in a vacuum $c = 2.997925 \times 10^{8} m s^{- 1}$ ; Avogadro constant $N_{A} = 6.022045 \times 10^{23} m o l^{- 1}$ ; Boltzmann constant $k_{B} = 1.3805 \times 10^{- 23} J K^{- 1}$ ; Faraday constant $F = 96500 C m o l^{- 1}$ ; Gas constant $R = 8.314 J K^{- 1} m o l^{- 1}$ ; $π = 3.14$ [2017/15m/8c]

In the following sequence of reactions, identify the products (A – H). (i) $S i C l_{4} + C H_{3} M g C l \to A \underset{pyrolysis}{\overset{controlled}{\to}} B$ (ii) $P C l_{5} + N H_{4} C l \underset{solvent (120°–150°C)}{\overset{heating in}{\to}} C \underset{in 300°C}{\overset{heating}{\to}} D$ (iii) $S C l_{2} + N H_{3} \overset{90^{\circ} C}{\to} E \underset{conc. alkali}{\overset{hydrolysis}{\to}} F$ (iv) $K I + F_{2} \overset{25^{\circ} C}{\to} G \overset{hydrolysis}{\to} H$ [2014/20m/6a]
Explain the structure and bonding in (i) Hexachlorocyclotriphosphazene (ii) Xenon hexafluoride. [2009/20m/8b]
Write the mechanism involved: (i) In the chain termination step during the cationic ring opening polymerization of hexachlorocyclotriphosphazines. (ii) In propagation step during the anionic ring Opening polymerization of octamethylcycloterasiloxanes. [2004/30m/4a]
What are phosphazene polymers? How a phosphazene polymer having $- O - C H_{2} - C F_{3}$ group is prepared? What are its important surgical uses? [2003/20m/6a]
Which compound A or B is expected to show lower stretching frequency for C = O group in the IR spectrum? (ii) How do trimeric phosphonitrillic halides compare with benzene in structure and reactivity?

[Figure: A = 4′-methoxyacetophenone ( $C H_{3} - C O - C_{6} H_{4} - O C H_{3}$ , para); B = 4′-nitroacetophenone ( $C H_{3} - C O - C_{6} H_{4} - N O_{2}$ , para)] [2001/15m/8b(i)]

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14.3] Silicates and silicones

11 questions

How are silicates classified? Predict the names and structures of the following silicates: (1) $S i O_{4}^{4 -}$ ion, (2) $S i_{2} O_{7}^{6 -}$ ion, (3) $S i_{3} O_{9}^{6 -}$ ion. [2026/10m/8b(ii)]
What are silicones? Mention some of their uses. How will you prepare hexamethyldisiloxane? Draw its structure. What happens if some ${(C H_{3})}_{3} S i C l$ is mixed with ${(C H_{3})}_{2} S i C l_{2}$ and hydrolysed? [2025/10m/8b]
Pyroxenes, amphiboles and phyllosilicates are well-known groups of silicates that occur in crust of the earth. Write the empirical formulae and draw the basic structural units of the above-mentioned silicates. [2023/10m/4d]
Write the general synthetic procedure of lower cyclosiloxanes like cyclic dimethylsiloxane trimer $[{(M e_{2} S i O)}_{3}]$ . Draw its structure. Why $M e S i C l_{3}$ is not used as starting material for its synthesis? [2022/10m/5e]
What are silicones? How are they obtained? Discuss the important properties and applications of organosilicon polymers. [2017/15m/7c]
Silicates produce a large number of silicate frameworks like $A l_{2} {(O H)}_{4} S i_{2} O_{5}$ ( $A$ ) $A l_{2} {(O H)}_{2} S i_{4} O_{10}$ ( $B$ ) $M g_{3} {(O H)}_{2} S i_{4} O_{10}$ ( $C$ ) $K A l_{2} {(O H)}_{2} S i_{3} A l O_{10}$ ( $D$ ) $N a_{12} [{(A l O_{2})}_{12} {(S i O_{2})}_{12}] \cdot 𝑥 H_{2} O$ ( $E$ ) Name the compounds $A$ , $B$ , $C$ , $D$ and $E$ . [2015/10m/8d]
In the following sequence of reactions, identify the products (A – H). (i) $S i C l_{4} + C H_{3} M g C l \to A \underset{pyrolysis}{\overset{controlled}{\to}} B$ (ii) $P C l_{5} + N H_{4} C l \underset{solvent (120°–150°C)}{\overset{heating in}{\to}} C \underset{in 300°C}{\overset{heating}{\to}} D$ (iii) $S C l_{2} + N H_{3} \overset{90^{\circ} C}{\to} E \underset{conc. alkali}{\overset{hydrolysis}{\to}} F$ (iv) $K I + F_{2} \overset{25^{\circ} C}{\to} G \overset{hydrolysis}{\to} H$ [2014/20m/6a]
“ $S i O_{4}$ tetrahedra form the framework of all silicates, including silica ( $S i O_{2}$ ).” Justify this statement with appropriate framework structures of ortho, pyro, cyclic, infinite chain, sheet and silica. [2014/20m/8a]
$R_{3} S i C l$ , $R_{2} S i C l_{2}$ , $R S i C l_{3}$ , (R = methyl) are used for making silicon polymers. Explain the roles of these compounds in the synthesis. [2013/10m/6a]
Give the reaction and show the structure of the polymer products formed from the following monomers: ${(C H_{3})}_{2} S i C l_{2}$ and $C H_{3} S i C l_{3}$ What will be the geometry of these polymers? How are these polymers used? [2003/20m/5a]
(i) Name the various types of ultramarines. Give their composition and uses. (ii) Rationalise the following transformations:

[Figure: (A) 2-vinylbicyclo[2.2.2]octan-2-ol skeleton drawn in perspective (bicyclo[2.2.2] cage, the carbon bearing OH and a vinyl group $C H = C H_{2}$ ; ring C=C not clearly shown [?]) –THF, reflux→ (B) cis-octalone: 3,4,4a,5,6,8a-hexahydronaphthalen-2(1H)-one type bicyclic ketone with both ring-junction H on dashed bonds (cis), C=O in one ring and a C=C in the other ring adjacent to a ring-junction carbon; (C) 6-vinylbicyclo[3.1.0]hex-2-ene (cyclopentene fused to a cyclopropane, the cyclopropane carbon bearing H and a vinyl group) –heat→ (D) bicyclo[3.2.1]octa-2,6-diene] [2003/20m/7c]

14.4] Interhalogen and noble gas compounds

20 questions

Complete the following reactions: (i) $S_{4} N_{4} \overset{S b C l_{5}}{\to}$ (ii) $X e F_{6} \overset{P t F_{5}}{\to}$ (iii) $B_{2} H_{6} \underset{- 120^{\circ} C}{\overset{N H_{3}}{\to}}$ (iv) $8 K r F_{2} + 2 A u \to$ (v) $X e O F_{4} + X e O_{3} \to$ [2025/10m/5g]
Draw all the possible structural dispositions of $C l F_{3}$ molecule. Establish logically which will be the most favoured disposition. Comment on the shape of $C l F_{3}$ molecule. [2024/10m/8b(i)]
Determine the electronic and molecular geometry of $[B r F_{5}]$ and ${[I C l_{2}]}^{-}$ interhalogen compounds. [2023/10m/3a]
Complete the following reactions and draw the structure of the major product(s) formed: (i) $2 X e F_{6} + S i O_{2} \overset{50^{\circ} C}{\to}$ ____ (ii) $N H_{4} N O_{3} \overset{520 K}{\to}$ ____ + ____ (iii) $N_{2} O + N a N H_{2} \overset{470 K}{\to}$ ____ (iv) $2 B_{2} H_{6} + 6 N H_{3} \overset{180^{\circ} C}{\to}$ ____ + ____ (v) $6 S C l_{2} + 16 N H_{3} \to$ ____ + ____ + ____. [2023/10m/6a]
(i) How $X e F_{6}$ can be separated from a mixture of $X e F_{2}$ , $X e F_{4}$ and $X e F_{6}$ ? (ii) Write the products with explanation $B_{2} H_{6} + 2 N H_{3} \to ?$ $B_{2} H_{6} + 2 M e_{3} N \to ?$ [2022/10m/6d]
Complete the following reactions: (i) $X e F_{4} + 12 H_{2} O \to$ ____ (ii) $X e F_{6} +$ ____ $\to X e O F_{4} + P F_{5}$ (iii) $X e O F_{4} +$ ____ $\to 2 X e O_{2} F_{2}$ (iv) $3 X e F_{2} + 2 {(S O_{3})}_{3} \to$ ____ (v) ____ $+ X e F_{2} \to {(C_{6} H_{5})}_{2} S F_{2} + X e$ [2021/10m/5e]
Justify that the interhalogen compound $B r F_{3}$ acts as an aprotic solvent and undergoes acid-base and neutralization reactions by giving examples. [2021/10m/8a]
What is the order of reactivity of the following interhalogens? $C l F_{3}$ , $I F_{7}$ , ClF, $B r F_{5}$ , IF. [2020/10m/7b(ii)]
Suggest a method for the preparation of Xenontrioxide. Complete the following reactions by balancing of atoms. $H \times e O_{4}^{-} + O H^{-} \to$ $B a_{2} \times e O_{6} + H_{2} S O_{4} \underset{- 5^{\circ} C}{\overset{}{\to}}$ [2019/10m/2c]
How would you prepare octafluoroxenate? Describe its structure and bonding. [2019/10m/5a]
Predict the product of the following reactions with justification: (A) ClF + $B F_{3} \to$ (B) ClF + CsF $\to$ (C) $C l F_{3} + B F_{3} \to$ (D) $I_{2} + B r_{2} \to$ [2018/10m/8a(i)]
Using valence bond theory justify the presence of two lone electron pairs in $X e F_{4}$ . [2017/15m/4c]
What are the main reasons for the formation of interhalogen compounds? Give one example of each type. Give the method of formation of $I F_{7}$ and draw its structure. [2016/15m/6a(i)]
Chlorine trifluoride, $C l F_{3}$ , is one of the most reactive compounds known. It can be made by heating $C l_{2}$ and $F_{2}$ in a closed container. (i) Draw the electron-dot structure of $C l F_{3}$ . (ii) What is the electron-pair geometry for $C l F_{3}$ ? (iii) Knowing that the molecule is polar, what can you conclude about the molecular geometry? (iv) Calculate the standard enthalpy of formation of gaseous $C l F_{3}$ , given the following bond energies: F—F: $159 k J m o l^{- 1}$ ; Cl—Cl: $243 k J m o l^{- 1}$ ; Cl—F: $255 k J m o l^{- 1}$ [2015/20m/6c]
Using hybridization, explain what is the shape of $X e O_{3}$ . Explain how VSEPR theory accounts for the distortion. [2012/10m/3c(ii)]
Give brief account on inter halogen compounds and discuss molecular structure of $I F_{7}$ . [2011/10m/7b(i)]
What are interhalogen compounds? How are they classified? Give structures of $I F_{5}$ and $I F_{7}$ . [2010/15m/5a]
Explain the structure and bonding in (i) Hexachlorocyclotriphosphazene (ii) Xenon hexafluoride. [2009/20m/8b]
Explain the structure and bonding in (i) iodine pentafluoride and (ii) polythiazyl. [2008/20m/8c]
Discuss the general features of aprotic solvents and the properties of $B r F_{3}$ . [2002/20m/7a]

14.5] Sulphur–nitrogen compounds

6 questions

Complete the following reactions: (i) $S_{4} N_{4} \overset{S b C l_{5}}{\to}$ (ii) $X e F_{6} \overset{P t F_{5}}{\to}$ (iii) $B_{2} H_{6} \underset{- 120^{\circ} C}{\overset{N H_{3}}{\to}}$ (iv) $8 K r F_{2} + 2 A u \to$ (v) $X e O F_{4} + X e O_{3} \to$ [2025/10m/5g]
Draw the structures of $S_{2} N_{2}$ , $S_{4} N_{2}$ , $S_{11} N_{2}$ , $S_{5} N_{6}$ and $I_{2} C l_{6}$ . [2025/10m/8a]
How tetrasulphur tetranitride ( $S_{4} N_{4}$ ) is prepared? Present its structure. What happens when $S_{4} N_{4}$ is subjected to chlorine? [2019/15m/6c]
Identify the products and draw the structure of A.

[Figure: Reaction scheme: $S_{2} C l_{2} + N H_{3}$ (1 : 2.67 ratio) –320 K, $C C l_{4}$ → A; A –490 K, over Ag wool→ B (colourless solid); A –550 K, over quartz wool→ C (golden-yellow solid)] [2018/10m/5d]

Give a short account of S-N compounds. [2010/10m/8a(i)]
Explain the structure and bonding in (i) iodine pentafluoride and (ii) polythiazyl. [2008/20m/8c]

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Last updated: 30 October 2026