#neet
- In pyrrole [figure: five-membered ring, N1 with H, carbons 2,3,4,5] the electron density is maximum on Answer: 3. 2 and 5 Key idea: in pyrrole the N lone pair is part of the aromatic sextet, so the ring carbons are electron-rich, most of all t... 1
- Which of the following compounds shall not produce propene by reaction with HBr followed by elimination or direct only elimination reaction? Answer: 2. H₂C=C=O Key idea: propene forms from a three-carbon alcohol or halide by elimination (or from cyclopropane by HBr ring opening to... 1
- Which one of the following nitro-compounds does not react with nitrous acid? Answer: 2. [structure shown in figure] Key idea: a nitroalkane reacts with HNO₂ only if it has an alpha-hydrogen. Primary give nitrolic acid... 1
- The central dogma of molecular genetics states that the genetic information flows from Answer: 2. DNA → RNA → Proteins Key idea: the central dogma: DNA is transcribed to mRNA, which is translated to protein. Information flows D... 1
- The correct corresponding order of names of four aldoses with configuration given below [four Fischer projections] respectively, is Answer: 3. D-erythrose, D-threose, L-erythrose, L-threose Key idea: D/L is decided by the OH on the lowest chiral carbon (right = D). Erythr... 1
- In the given reaction [benzene + cyclohexene, HF, 0 C -> P] the product P is Answer: 2. [structure shown in figure] Key idea: HF protonates the alkene to give a carbocation, which alkylates benzene (Friedel-Crafts alk... 1
- A given nitrogen-containing aromatic compound A reacts with Sn/HCl, followed by HNO_2 to give an unstable compound B. B, on treatment with phenol, forms a beautiful coloured compound C with the molecular formula C_12H_10N_2O. The structure of compoun… Answer: 1. nitrobenzene ( C₆H₅NO₂ ) Key idea: nitro compound → amine → diazonium salt → azo dye. C₆H₅NO₂xrightarrowSn/HClC₆H₅NH₂ C₆H₅NH₂xrig... 1
- Consider the reactionCH_3CH_2CH_2Br + NaCN → CH_3CH_2CH_2CN + NaBrThis reaction will be the fastest in Answer: 2. N,N' -dimethylformamide (DMF) Key idea: this is an S_N2 reaction on a primary halide, which is fastest in a polar aprotic solvent... 1
- The correct structure of the product A formed in the reaction [cyclohex-2-enone, H_2 (gas, 1 atmosphere), Pd/carbon, ethanol → A] is Answer: 1. [structure shown in figure] Key idea: H₂ with Pd/C at 1 atm reduces the C=C bond selectively; the C=O is not reduced under these... 1
- Which among the given molecules can exhibit tautomerism? Answer: 4. III only Key idea: keto-enol tautomerism needs an alpha-H, and the enol must be able to form (a double bond at a bridgehead is no... 1
- The correct order of strengths of the carboxylic acids [I, II, III shown] is Answer: 1. II > III > I Key idea: an electron-withdrawing atom near COOH stabilises the carboxylate and raises acidity; the effect weakens w... 1
- The compound that will react most readily with gaseous bromine has the formula Answer: 4. C₃H₆ Key idea: gaseous Br₂ adds readily across a C=C bond; a more electron-rich alkene reacts faster. C₃H₆ (propene) beats C₂H₄ b... 1
- Which one of the following compounds shows the presence of intramolecular hydrogen bond? Answer: 2. Cellulose Key idea: the key gives cellulose; the stem is partly unreadable, so the answer follows the key. HCN, concentrated acet... 1
- The molar conductivity of a [obscured] solution of AgNO_3 with electrolytic conductivity of 5.76×10^-3 S cm^-1 at 298 K is Answer: 1. 11.52 S cm ² /mol Key idea: molar conductivity Lambda_m=kappa×1000/M (S cm ² mol ⁻¹ , kappa in S cm ⁻¹ , M in mol/L). Lambda_m=fr... 1
- The decomposition of phosphine [obscured] on tungsten at low pressure is a [obscured] reaction. It is because the Answer: 4. rate is proportional to the surface coverage Key idea: on a metal surface at low pressure the surface is not saturated, so the ra... 1
- The coagulation values in millimoles per litre of the electrolytes used for the coagulation of As_2S_3 are given below:I. (NaCl) = 52, II. (BaCl_2) = 0.69,III. (MgSO_4) = 0.22The correct order of their coagulating power is Answer: 2. III > II > I Key idea: coagulating power is inversely proportional to coagulation value (the minimum amount needed). Smaller valu... 1
- During the electrolysis of molten sodium chloride, the time required to produce 0.10 mol of chlorine gas using a current of 3 amperes is Answer: 1. 110 minutes Key idea: 2Cl^-→ Cl₂+2e^- , so 1 mol Cl₂ needs 2 F. Q=0.10×2×96500=19300\ C t=Q/I=19300/3≈6433\ s≈107\ min≈110\ min T... 1
- For a sample of perfect gas when its pressure is changed isothermally from p_i to p_f, the entropy change is given by Answer: 1. Δ S = nRln(p_i/p_f) Key idea: for an isothermal ideal gas, Δ S=nRln(V_f/V_i) , and V∝1/p . Δ S=nRlnV_f/V_i=nRlnp_i/p_f The T does... 1
- The van't Hoff factor (i) for a dilute aqueous solution of the strong electrolyte barium hydroxide is Answer: 3. 3 Key idea: i equals the number of ions per formula unit on complete dissociation. mathrmBa(OH)₂→ Ba²⁺+2OH^- This gives 3 ions, s... 1
- The percentage of pyridine (C_5H_5N) that forms pyridinium ion (C_5H_5N^+H) in a 0.10 M aqueous pyridine solution (K_b for C_5H_5N = 1.7×10^-9) is Answer: 1. 0.013% Key idea: for a weak base, α=√(K_b/C) . α=sqrtfrac1.7×10⁻⁹0.10=sqrt1.7×10⁻⁸=1.3×10⁻⁴ Percentage = 1.3×10⁻⁴×100=0.013% . 1
- In calcium fluoride, having the fluorite structure, the coordination numbers for calcium ion (Ca^2+) and fluoride ion (F^-) are Answer: 2. 8 and 4 Key idea: in the fluorite structure, Ca²⁺ forms an fcc lattice and F^- occupies all tetrahedral holes. Each F^- is surrou... 1
- Smooth muscles are Answer: 4. involuntary, fusiform, non-striated Smooth muscles are involuntary, spindle-shaped (fusiform), uninucleate and non-striated. They... 1
- The suspension of slaked lime in water is known as Answer: 2. milk of lime Key idea: Ca(OH)₂ is only sparingly soluble in water. A suspension of slaked lime in water looks milky, so it is cal... 1
- Oxidative phosphorylation is Answer: 3. formation of ATP by energy released from electrons removed during substrate oxidation Oxidative phosphorylation is the formation... 1