NEET 2023 Chemistry Questions with Solutions

Explanation

Hofmann bromamide reaction of acetamide gives methylamine, a primary amine. Reduction of nitrile (CH3CN) with LiAlH4 also gives a primary amine. Reduction of acetamide with LiAlH4 gives ethylamine, which is also a primary amine. However, reduction of isocyanide (CH3NC) gives a secondary amine, therefore reaction (3) does NOT give a primary amine.

Explanation

Metallic sodium dissolves in liquid ammonia to produce solvated electrons, giving a deep blue paramagnetic solution. The colour and paramagnetism are due to these solvated electrons, not because of amide formation. Therefore, Assertion A is true but Reason R is false.

Explanation

When both nitrogen and sulphur are present in Lassaigne’s extract, sodium thiocyanate is formed. On treatment with Fe3+, blood red coloured ferric thiocyanate complex [Fe(SCN)]2+ is produced.

Explanation

Conductivity κ = 0.0210 ohm−1 cm−1 Resistance R = 60 ohm Cell constant = κ × R = 0.0210 × 60 = 1.26 cm−1 Hence, the correct answer is 1.26 cm−1.

Explanation

Activation energy is the minimum extra energy required for reactants to reach threshold energy. Hence Reason R is true. However, every reaction requires at least some activation energy, so Assertion A is false.

Explanation

In heterogeneous catalysis, the catalyst and reactants are in different phases. In the Haber process, nitrogen and hydrogen are gases while finely divided iron is a solid catalyst. Hence, it is an example of heterogeneous catalysis.

Explanation

The halogen atom X is attached to the carbon adjacent to a carbon-carbon double bond. Such compounds are called allylic halides.

Explanation

Benzene diazonium chloride reacts with Cu₂Br₂/HBr to form bromobenzene (Sandmeyer reaction). Bromobenzene reacts with Mg/dry ether to form phenyl magnesium bromide, which on hydrolysis with water gives benzene.

Explanation

Helium is used in diving apparatus because it has very low solubility in blood and prevents bends caused by nitrogen dissolution. The statement that helium has high solubility in oxygen is false.

Explanation

If B atoms form a close packed structure containing n atoms, then the number of tetrahedral voids is 2n. Since A occupies 1/3 of tetrahedral voids, number of A atoms = 2n/3. Thus, ratio A : B = 2n/3 : n = 2 : 3. Therefore, the formula is A₂B₃ and x + y = 2 + 3 = 5.

Explanation

For a given azimuthal quantum number l, the magnetic quantum number m can have values from -l to +l. Hence, the total number of permissible values is: n_m = 2l + 1 Rearranging: l = (n_m - 1)/2 Therefore, option (A) is correct.

Explanation

Check the number of electrons around the central atom: NH3 → N has 8 electrons. AlCl3 → Al has 6 electrons. BeCl2 → Be has 4 electrons. CCl4 → C has 8 electrons. PCl5 → P has 10 electrons. Species not having octet are: AlCl3, BeCl2 and PCl5. Total = 3. Hence, option (A) is correct.

Explanation

For molecules up to N2, due to s-p mixing, the energy order is: σ1s < σ*1s < σ2s < σ*2s < π2px = π2py < σ2pz < π*2px = π*2py < σ*2pz Therefore, option (A) is correct.

Explanation

Pyridine contains: - 6 σ bonds in the ring - 5 C–H σ bonds Total σ bonds = 11 There are 3 π bonds in the aromatic ring. Nitrogen atom contains 1 lone pair. Hence, the correct answer is 11, 3, 1. Therefore, option (C) is correct.

Explanation

Intermolecular forces include: - Dipole-dipole forces - Dipole-induced dipole forces - Hydrogen bonding - Dispersion forces Covalent bonding is an intramolecular force, not an intermolecular force. Hence, A, B, C and E are correct. Therefore, option (C) is correct.

Explanation

Evaluate each statement: A. Correct — Hydrogen reduces some metal oxides. B. Correct — Heavy water is used in studying reaction mechanisms. C. Correct — Hydrogenation converts oils into saturated fats. D. Incorrect — H-H bond dissociation enthalpy is not the lowest. E. Incorrect — Hydrogen reduces oxides of metals less active than iron. Thus, D and E are NOT correct. Therefore, option (C) is correct.

Explanation

Neoprene is formed by polymerization of chloroprene (2-chloro-1,3-butadiene), whose structure is H₂C = C(Cl) − CH = CH₂. Therefore, option (B) is correct.

Explanation

Veronal is a barbiturate tranquilizer. Chlordiazepoxide and Valium belong to benzodiazepines, while Meprobamate is a carbamate tranquilizer.

Explanation

Nitrogen gains three electrons to achieve the nearest noble gas configuration (Ne), forming N³⁻, which has the largest ionic radius among the given ions.

Explanation

Statement B is correct as it gives the correct electron mass. Statement C is correct because isotopes have the same electronic configuration and hence similar chemical properties. Statement E is also correct according to Dalton's atomic theory. Statements A and D are incorrect.

Explanation

3-Methylbutan-2-ol reacts with HBr via carbocation formation followed by rearrangement to form the more stable tertiary carbocation. Bromide attack then gives 2-bromo-2-methylbutane as the major product.

Explanation

Heating sodium ethanoate with sodium hydroxide in the presence of calcium oxide (soda lime) produces methane: CH3COONa + NaOH → CH4 + Na2CO3 Molar mass of methane (CH4) = 16 g/mol Weight of 2 moles = 2 × 16 = 32 g. Hence, option (B) is correct.

Explanation

A Lewis acid is an electron pair acceptor. BF3 is electron deficient because boron has only six electrons in its valence shell and can accept an electron pair. NH3, H2O and OH− possess lone pairs and act as Lewis bases. Hence, option (C) is correct.

Explanation

Zn-Hg with concentrated HCl carries out Clemmensen reduction, which converts carbonyl groups (>C=O) into methylene groups (−CH2−). Both ketone groups in the substrate are reduced to alkyl groups, giving the fully reduced hydrocarbon product. Hence, option (A) is correct.

Explanation

A homoleptic complex contains only one type of ligand attached to the central metal atom. Potassium trioxalatoaluminate (III) contains only oxalato ligands, hence it is homoleptic.

Explanation

Cyclohexanone reacts with HCN to form cyanohydrin. On hydrolysis with concentrated H₂SO₄ and heat, the nitrile group converts into carboxylic acid followed by dehydration to form cyclohexene carboxylic acid. Hence option (D) is correct.

Explanation

20 g of 20% pure limestone contains: 20 × (20/100) = 4 g CaCO₃ Molar mass of CaCO₃ = 40 + 12 + (16 × 3) = 100 g/mol From the reaction: 100 g CaCO₃ produces 44 g CO₂ Therefore, 4 g CaCO₃ produces = (44/100) × 4 = 1.76 g CO₂ Hence, the correct answer is 1.76 g.

Explanation

Given: Rate = k[A]²[B] If concentration of A is tripled: New rate = k(3[A])²[B] = 9k[A]²[B] Thus, the rate increases by a factor of 9. Hence, the correct answer is option (C).

Explanation

The relation between Gibbs free energy and cell potential is: ΔᵣG = −nFE°cell Here, E°cell is an intensive property and does not depend on the amount of substance, whereas ΔᵣG is an extensive property and depends on the number of moles involved in the reaction. Therefore, ΔᵣG depends on n. Hence, both Assertion and Reason are true, and Reason correctly explains Assertion.

Explanation

The complex [CoCl2(en)2]NO3 is the most stable because ethylenediamine (en) is a bidentate ligand and forms chelate rings with cobalt. Due to the chelate effect, complexes containing multidentate ligands are more stable than those containing only monodentate ligands.

Explanation

Compounds/species obeying Huckel's rule must contain (4n + 2) π electrons and be cyclic, planar, and conjugated. The aromatic species among the given compounds are i, iv, v, and vii. Hence, the total number of species obeying Huckel's rule is 4.

Explanation

In an fcc unit cell, an edge-centred octahedral void is shared among four adjacent unit cells. Therefore, the fraction of one edge-centred octahedral void belonging to a single unit cell is 1/4.

Explanation

The relation between enthalpy change and internal energy change for gaseous reactions is: ΔH = ΔU + Δn₍g₎RT where Δn₍g₎ is the change in moles of gaseous species.

Explanation

Balancing the reaction in acidic medium gives: Cr₂O₇²⁻ + 3SO₃²⁻ + 8H⁺ → 2Cr³⁺ + 3SO₄²⁻ + 4H₂O Hence, a = 1, b = 3 and c = 8.

Explanation

For the reaction: A + B ⇌ C + D Kc = [C][D]/[A][B] = (10 × 6)/(2 × 3) = 10 Using: ΔG° = −RT ln K = −(2)(300)ln(10) = −600 × 2.303 = −1381.80 cal

Explanation

Pumice stone contains gas dispersed in a solid medium and is classified as a solid foam or solid sol in colloidal systems. According to the given answer key, option (C) is correct.

Explanation

Tollens' reagent oxidizes the aldehyde group to carboxylate ion in alkaline medium, while the ketone group remains unaffected. Therefore, the aldehyde is converted into COO⁻ and the ketone remains intact. Hence option (C) is the major product.

Explanation

CH₃CHO on reduction with LiAlH₄ followed by hydrolysis gives ethanol [A]. Ethanol on dehydration with concentrated H₂SO₄ and heat gives ethene [B]. Ethene reacts with HBr to form bromoethane [C]. Bromoethane reacts with bromobenzene in presence of Na/dry ether through Wurtz-Fittig reaction to form ethyl benzene [D]. Therefore, the correct option is (1).

Explanation

Dehydration of alcohols under acidic conditions proceeds through formation of a carbocation intermediate. The compound in option (B) forms a more stable secondary carbocation and undergoes dehydration most readily. Electron-withdrawing nitro groups in the other options destabilize the carbocation intermediate, reducing the ease of dehydration.

Explanation

The given compound is benzyl phenyl ether. Ethers react with HI under heating to undergo cleavage. In aryl-alkyl ethers, the alkyl-oxygen bond breaks because the aryl-oxygen bond has partial double bond character due to resonance. Therefore, benzyl iodide (C6H5CH2I) and phenol (C6H5OH) are formed.

Explanation

In the blast furnace, Fe₂O₃ is first reduced to Fe₃O₄ and then to FeO before metallic iron is formed. The direct conversion: Fe₂O₃ + CO → 2FeO + CO₂ does not occur in the 900 K to 1500 K range as written. Other reactions listed are important processes in the blast furnace: - FeO is reduced to Fe by CO. - CO is regenerated by reaction of carbon with CO₂. - CaO reacts with SiO₂ impurity to form slag (CaSiO₃). Hence, option (A) is correct.