#neet
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- Which of the following is not observed during apoplastic pathway ? Answer: 4. The movement is aided by cytoplasmic streaming In the apoplastic pathway water moves only through cell walls and intercellular sp... 1
- The device which can remove particulate matter present in the exhaust from a thermal power plant is : Answer: 4. Electrostatic Precipitator An electrostatic precipitator removes particulate matter from the exhaust of thermal power plants. Its... 1
- Which one of the following never occurs during mitotic cell division ? Answer: 4. Pairing of homologous chromosomes Pairing of homologous chromosomes (synapsis) is a feature of meiosis I, never of mitosis. In mi... 1
- Hydrocolloid carrageen is obtained from : Answer: 4. Rhodophyceae only Carrageen is a hydrocolloid obtained from red algae (Rhodophyceae), such as Chondrus. Brown algae (Phaeophyceae... 1
- Read the following statements about the vascular bundles :(a) In roots, xylem and phloem in a vascular bundle are arranged in an alternate manner along the different radii.(b) Conjoint closed vascular bundles do not possess cambium(c) In open vascula… Answer: 3. (b), (c), (d) and (e) Only Check each statement against NCERT; the key says statement (a) does not hold, so the answer is (b), (c... 1
- DNA polymorphism forms the basis of : Answer: 4. Both genetic mapping and DNA finger printing DNA polymorphism means variation in DNA sequence between individuals. It is the basi... 1
- Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).Assertion (A) :Polymerase chain reaction is used in DNA amplificationReason (R) :The ampicillin resistant gene is used as a selectable marker to… Answer: 3. Both (A) and (R) are correct but (R) is not the correct explanation of (A) Check each statement and then the link between them. A... 1
- The appearance of recombination nodules on homologous chromosomes during meiosis characterizes : Answer: 4. Sites at which crossing over occurs Recombination nodules are protein-rich structures seen in the pachytene stage on the synapton... 1
- The flowers are Zygomorphic in :(a) Mustard(b) Gulmohar(c) Cassia(d) Datura(e) ChillyChoose the correct answer from the options given below : Answer: 3. (b), (c) Only Zygomorphic flowers can be divided into two equal halves in only one vertical plane. Gulmohar and Cassia (family Fa... 1
- Match List - I with List - II.List - I: (a) Li (b) Na (c) KOH (d) CsList - II: (i) absorbent for carbon dioxide (ii) electrochemical cells (iii) coolant in fast breeder reactors (iv) photoelectric cellChoose the correct answer from the options given… Answer: 1. (a) - (ii), (b) - (iii), (c) - (i), (d) - (iv) Key idea: recall the uses of alkali metals and their compounds. Li: electrochemica... 1
- Given below are half cell reactions :MnO_4^- + 8H^+ + 5e^- → Mn^2+ + 4H_2O,E^°_Mn^2+/MnO_4^- = -1.510 V1/2O_2 + 2H^+ + 2e^- → H_2O,E^°_O_2/H_2O = +1.223 VWill the permanganate ion, MnO_4^- liberate O_2 from water in the presence of an acid ? Answer: 2. Yes, because E^°_cell = +0.287 V Key idea: a reaction is spontaneous if E^°_cell>0 , using the reduction potentials of the two ha... 1