Chemistry
- The right option for the mass of CO_2 produced by heating 20 g of 20% pure limestone is (Atomic mass of Ca = 40)CaCO_3 1200\ K CaO + CO_2 Answer: 3. 1.76 g Key idea: Only the pure CaCO₃ decomposes; find its moles and use 1:1 mole ratio with CO₂ . Pure CaCO₃ = 20 × 20/100 = 4 g.... 1
- If radius of second Bohr orbit of the He^+ ion is 105.8 pm, what is the radius of third Bohr orbit of Li^2+ ion ? Answer: 2. 158.7 pm Key idea: Bohr radius r_n=0.529 n²/Z Å, so r∝ n²/Z . He^+ , n = 2: r=a₀×4/2=2a₀=105.8 pm, so a₀=52.9 pm. mathrmLi²⁺ , n... 1
- For a first order reaction A → Products, initial concentration of A is 0.1 M, which becomes 0.001 M after 5 minutes. Rate constant for the reaction in min^-1 is Answer: 3. 0.9212 Key idea: for a first order reaction k=2.303/tlog[A]₀/[A] . k=2.303/5log0.1/0.001=2.303/5×2=0.9212\ mathrmmin⁻¹ . 1
- The order of energy absorbed which is responsible for the color of complexes(A) [Ni(H_2O)_2(en)_2]^2+(B) [Ni(H_2O)_4(en)]^2+ and(C) [Ni(en)_3]^2+is Answer: 4. (C) > (A) > (B) Key idea: stronger field ligands cause larger splitting Δ_o , so the complex absorbs higher energy light. Ligand... 1
- In the neutral or faintly alkaline medium, KMnO_4 oxidises iodide into iodate. The change in oxidation state of manganese in this reaction is from Answer: 2. +7 to +4 Key idea: in neutral or weakly alkaline medium permanganate is reduced to MnO₂ . 2MnO₄^-+H₂O+I^-→2MnO₂+2OH^-+IO₃^- . Mn... 1
- Gadolinium has a low value of third ionisation enthalpy because of Answer: 3. high exchange enthalpy Key idea: exchange enthalpy stabilises half-filled subshells. Gd is [Xe]4f⁷5d¹6s² . Removing the third ele... 1
- Match List - I with List - II.List - I (Ores): (a) Haematite (b) Magnetite (c) Calamine (d) KaoliniteList - II (Composition): (i) Fe_3O_4 (ii) ZnCO_3 (iii) Fe_2O_3 (iv) [Al_2(OH)_4Si_2O_5]Choose the correct answer from the options given below : Answer: 3. (a) - (iii), (b) - (i), (c) - (ii), (d) - (iv) Key idea: recall ore compositions. Haematite: Fe₂O₃ (iii) Magnetite: Fe₃O₄ (i) Cal... 1
- 3O_2(g) ⇌ 2O_3(g)for the above reaction at 298 K, K_c is found to be 3.0 × 10^-59. If the concentration of O_2 at equilibrium is 0.040 M then concentration of O_3 in M is Answer: 2. 4.38 × 10⁻³² Key idea: K_c=[O₃]²/[O₂]³ . [O₃]²=3.0×10⁻⁵⁹×(0.040)³=3.0×10⁻⁵⁹×6.4×10⁻⁵=1.92×10⁻⁶³ . [O₃]=sqrt1.92×10⁻⁶³=4.38×10⁻³²... 1
- Compound X on reaction with O_3 followed by Zn/H_2O gives formaldehyde and 2-methyl propanal as products. The compound X is : Answer: 2. 3-Methylbut-1-ene Key idea: ozonolysis cuts the C=C bond and puts a C=O on each carbon. Working backwards: HCHO and mathrm(CH₃)₂C... 1
- The product formed from the following reaction sequence is[benzonitrile] [(iii) H_2O](i) LiAlH_4, H_2O;\ (ii) NaNO_2 + HCl Answer: 1. [structure in figure] Key idea: follow each step. LiAlH₄ reduces the nitrile C₆H₅CN to the primary amine C₆H₅CH₂NH₂ (benzylamine)... 1
- Given below are two statements :Statement I :In Lucas test, primary, secondary and tertiary alcohols are distinguished on the basis of their reactivity with conc. HCl + ZnCl_2, known as Lucas Reagent.Statement II :Primary alcohols are most reactive a… Answer: 4. Statement I is correct but Statement II is incorrect. Key idea: Lucas reagent (conc. HCl + ZnCl₂ ) works via carbocation formatio... 1
- Which one of the following is not formed when acetone reacts with 2-pentanone in the presence of dilute NaOH followed by heating ? Answer: 3. [structure in figure] Key idea: in crossed aldol condensation with NaOH, either ketone can give the enolate and either can be the... 1
- The pollution due to oxides of sulphur gets enhanced due to the presence of :(a) particulate matter(b) ozone(c) hydrocarbons(d) hydrogen peroxideChoose the most appropriate answer from the options given below : Answer: 3. (a), (b), (d) only Key idea: SO₂ is converted to SO₃ and then to sulphuric acid faster when oxidants or surfaces are present. Par... 1
- Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).Assertion (A) : ICl is more reactive than I_2.Reason (R) : I-Cl bond is weaker than I-I bond.In the light of the above statements, choose the mo… Answer: 2. Both (A) and (R) are correct and (R) is the correct explanation of (A) Key idea: interhalogen compounds are more reactive than th... 1
- Find the emf of the cell in which the following reaction takes place at 298 KNi(s) + 2Ag^+ (0.001\ M) → Ni^2+ (0.001\ M) + 2Ag(s)(Given that E^°_cell = 10.5 V, 2.303 RT/F = 0.059 at 298 K) Answer: Dropped in the official answer key: full marks to every candidate Key idea: use the Nernst equation E=E^°-0.059/nlog Q . Reaction: m... 1
- In one molal solution that contains 0.5 mole of a solute, there is Answer: 3. 500 g of solvent Key idea: molality = moles of solute per kg of solvent. 1\ m=0.5/w with w in kg gives w=0.5 kg =500 g of solvent... 1
- A 10.0 L flask contains 64 g of oxygen at 27°C. (Assume O_2 gas is behaving ideally). The pressure inside the flask in bar is(Given R = 0.0831 L bar K^-1 mol^-1) Answer: 1. 4.9 Key idea: use PV=nRT . n=64/32=2 mol, T=300 K. P=nRT/V=2×0.0831×300/10=4.986≈4.9 bar (nearest option is 4.9; 4.986 bar is 4.9... 1
- Copper crystallises in fcc unit cell with cell edge length of 3.608 × 10^-8 cm. The density of copper is 8.92 g cm^-3. Calculate the atomic mass of copper. Answer: 2. 63.1 u Key idea: density ρ=ZM/a³N_A , so M=ρ a³N_A/Z . fcc has Z = 4. a³=(3.608×10⁻⁸)³=4.697×10⁻²³\ cm³ . M=dfrac8.92×4.697×10⁻²³... 1
- The correct IUPAC name of the following compound is :[skeletal structure with Cl, OH, Br and a methyl branch] Answer: 2. 1-bromo-5-chloro-4-methylhexan-3-ol Key idea: choose the longest chain containing the -OH group, give -OH the lowest locant, then... 1
- Identify the incorrect statement from the following. Answer: 1. The shapes of d_xy , d_yz , and d_zx orbitals are similar to each other ; and d_(x²-y²) and d_z² are similar to each other. Key i... 1
- The incorrect statement regarding enzymes is : Answer: 4. Enzymes are polysaccharides. Key idea: enzymes are (almost all) globular proteins, not polysaccharides. Statements 1 to 3 are tru... 1
- Match List - I with List - II.List - I (Drug class): (a) Antacids (b) Antihistamines (c) Analgesics (d) AntimicrobialsList - II (Drug molecule): (i) Salvarsan (ii) Morphine (iii) Cimetidine (iv) SeldaneChoose the correct answer from the options given… Answer: 3. (a) - (iii), (b) - (iv), (c) - (ii), (d) - (i) Key idea: match each drug class with a standard example. Antacids: cimetidine (iii... 1
- The given graph is a representation of kinetics of a reaction.[Graph: y versus x at constant temperature T]The y and x axes for zero and first order reactions, respectively are Answer: 4. zero order ( y = rate and x = concentration), first order ( y = t_(1/2) and x = concenration) Key idea: a horizontal line means y... 1
- Which of the following p-V curve represents maximum work done ? Answer: 3. [graph in figure] Key idea: work done by the gas equals the area under the p-V curve, so find the graph with the largest area. Gr... 1