NEET 2021 Chemistry Questions with Solutions

Explanation

For N close-packed atoms: - Number of octahedral voids = N - Number of tetrahedral voids = 2N A hexagonal primitive unit cell contains 6 atoms. Therefore: - Octahedral voids = 6 - Tetrahedral voids = 12 Hence the correct answer is 12, 6.

Explanation

According to Boyle's law, at constant temperature: P ∝ 1/V Therefore, PV = k where k = nRT. Hence, the graph between pressure and volume is a rectangular hyperbola. Since k = nRT increases with temperature, higher temperature curves lie above lower temperature curves. Therefore, option (A) is correct.

Explanation

Tyndall effect is shown by colloidal solutions. Urea, NaCl, and glucose form true solutions, while starch forms a colloidal solution.

Explanation

Tritium (³H) undergoes beta decay and emits β⁻ particles.

Explanation

According to Saytzeff's rule, the major product in elimination reactions is the more substituted alkene. Hence pent-2-ene is the major product.

Explanation

Using Kohlrausch’s law: Λ°(CH₃COOH) = Λ°(CH₃COONa) + Λ°(HCl) − Λ°(NaCl) = 91.0 + 426.16 − 126.45 = 390.71 S cm² mol⁻¹.

Explanation

Down Group 17, bond length increases from HF to HI, causing bond strength to decrease. Therefore proton release becomes easier and acid strength increases: HI > HBr > HCl > HF.

Explanation

For the compound name **2,6-Dimethyldec-4-ene**: - **dec** → longest chain contains 10 carbon atoms. - **4-ene** → double bond must be present between carbon 4 and carbon 5. - **2,6-dimethyl** → methyl (-CH₃) substituents must be attached at carbon 2 and carbon 6. Among the given structures, only **Option (B)** satisfies all these conditions correctly. Hence, the correct answer is **Option (B)**.

Explanation

Bond length increases from C-F to C-I, reducing bond strength. Hence bond enthalpy decreases in the order: CH3-F > CH3-Cl > CH3-Br > CH3-I.

Explanation

For salt of weak acid and weak base: pH = 7 + 1/2(pKa - pKb) = 7 + 1/2(4.77 - 3.27) = 7.75

Explanation

Osmotic pressure is given by: $$\pi = iCRT$$ For non-electrolytes like glucose, urea, and sucrose: $$i = 1$$ Since all solutions are prepared in the same volume of water and at the same temperature: $$\pi \propto C \propto \text{number of moles}$$ Calculate moles: For glucose: $$M = 180\,g\,mol^{-1}$$ $$n = \frac{10}{180} = 0.0556$$ For urea: $$M = 60\,g\,mol^{-1}$$ $$n = \frac{10}{60} = 0.1667$$ For sucrose: $$M = 342\,g\,mol^{-1}$$ $$n = \frac{10}{342} = 0.0292$$ Thus, $$\text{Urea} > \text{Glucose} > \text{Sucrose}$$ Therefore, decreasing order of osmotic pressure: $$P_2 > P_1 > P_3$$ Hence, option **(B)** is correct.

Explanation

Body centred unit cells exist in cubic, tetragonal and orthorhombic crystal systems. Therefore total number = 3.

Explanation

As per NCERT, the maximum temperature achieved in a blast furnace is approximately 2170 K, so the closest option is 2200 K.

Explanation

ΔH = Eb − Ea = -4.2 kJ/mol, so products are at lower energy than reactants (exothermic reaction). Activation energy is positive, so graph must show an energy barrier followed by lower product energy. Hence option (C).

Explanation

In presence of peroxide, HBr follows anti-Markovnikov addition via free radical mechanism. Bromine attaches to the less substituted carbon.

Explanation

A metal displacement reaction occurs when a more reactive metal displaces a less reactive metal from its compound. In reaction (3), aluminium displaces chromium from chromium oxide: Cr₂O₃ + 2Al → Al₂O₃ + 2Cr This is an example of metal displacement (thermite-type reaction). Reaction (1) and reaction (2) are decomposition reactions. Reaction (4) is a hydrogen displacement reaction where iron displaces hydrogen from HCl. Therefore, option C is correct.

Explanation

Aspirin and Paracetamol are classified as non-narcotic analgesics because they relieve pain without causing sleep or addiction. Morphine and Heroin are classified as narcotic analgesics because they relieve pain but can induce sleep and addiction. Therefore, both Statement I and Statement II are false, so option (C) is correct.

Explanation

Distillation is used for purification of low boiling metals like mercury.

Explanation

Primary amines react with Hinsberg reagent to form sulphonamides containing acidic hydrogen, which dissolve in alkali. Therefore option (D) is correct.

Explanation

Due to the small size and high polarising power of Be²⁺, BeCl₂ shows covalent character and is soluble in organic solvents.

Explanation

The least stable conformer of ethane is the eclipsed form where the dihedral angle is 0°.

Explanation

Carbon = 78/12 = 6.5 moles, Hydrogen = 22/1 = 22 moles. Ratio = 1:3.38 ≈ 1:3 → empirical formula = CH3.

Explanation

Teflon is formed by addition polymerisation of tetrafluoroethene. Dacron, Nylon-66, and Novolac are condensation polymers.

Explanation

For an ideal gas, internal energy depends only on temperature. Under isothermal conditions: $T = \text{constant} \Rightarrow \Delta U = 0$ For an irreversible process, total entropy always increases: $\Delta S_{\text{total}} > 0$ Hence, $\Delta S_{\text{total}} \neq 0$ Therefore, the correct option is **(4)**.

Explanation

NaBH4 reduces aldehydes/ketones to alcohols but does not reduce esters. Hence only ketone group is reduced.

Explanation

For group 16 hydrides, acidic strength increases down the group because bond strength decreases: $\mathrm{H_2O < H_2S < H_2Se < H_2Te}$ (increasing acidic strength) Since stronger acids have lower $pK_a$ values, the $pK_a$ values should decrease down the group, not increase. Thus statement (3) is incorrect. Options (A), (B), and (4) follow the correct trends.

Explanation

SO2 oxidation contributes to tropospheric pollution, HOCl photolysis causes ozone depletion, acid rain reacts with CaCO3, and NO2 photolysis contributes to photochemical smog.

Explanation

Λ°m(CH₃COOH) = Λ°H⁺ + Λ°CH₃COO⁻ = 350 + 50 = 400 S cm² mol⁻¹ α = Λm / Λ°m = 20 / 400 = 1/20 Ka = Cα² / (1-α) = 0.007 × (1/20)² / (19/20) ≈ 1.75 × 10⁻⁵ mol L⁻¹ Hence option (D) is correct.

Explanation

Moles of O₂ = 4/32 = 1/8 mol Moles of H₂ = 2/2 = 1 mol Total moles = 1/8 + 1 = 9/8 mol Using PV = nRT: P = (nRT)/V = (9/8 × 0.082 × 273)/1 = 25.18 atm Hence option (D) is correct.

Explanation

For an ideal solution, apply Raoult’s law: x(benzene) = 3/(3+2) = 3/5 x(octane) = 2/(3+2) = 2/5 Total vapour pressure: P = x(benzene)P°(benzene) + x(octane)P°(octane) = (3/5 × 280) + (2/5 × 420) = 168 + 168 = 336 mm Hg Hence, option (D) is correct.

Explanation

Isoelectronic species contain the same number of electrons. Fe²⁺ → 26 - 2 = 24 electrons Mn²⁺ → 25 - 2 = 23 electrons These are not equal, so they are not isoelectronic. Checking other options: O²⁻ → 8 + 2 = 10 electrons F⁻ → 9 + 1 = 10 electrons Na⁺ → 11 - 1 = 10 electrons Mg²⁺ → 12 - 2 = 10 electrons Mn²⁺ → 25 - 2 = 23 electrons Fe³⁺ → 26 - 3 = 23 electrons Thus, option (A) is correct.

Explanation

Aryl diazonium salts are reduced to benzene derivatives when treated with ethanol. Here, tribromobenzenediazonium chloride reacts with ethanol to replace the diazonium group by hydrogen, forming 1,3,5-tribromobenzene. Hence, R = C2H5OH.

Explanation

For an Arrhenius plot of ln k versus 1/T, slope = −Ea/R. So, Ea = −(slope) × R = (5 × 10^3) × 8.314 = 41570 J mol⁻¹ = 41.5 kJ mol⁻¹ Hence, the correct option is B (41.5 kJ mol⁻¹).

Explanation

(a) Benzene + CO/HCl in presence of AlCl3/CuCl → Gattermann-Koch reaction (b) Methyl ketone + NaOX → Haloform reaction (c) Alcohol + carboxylic acid + conc. H2SO4 → Esterification (d) Carboxylic acid + X2/Red P → Hell-Volhard-Zelinsky reaction Correct matching: (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i).

Explanation

Correct matching: - Protein $\rightarrow$ Peptide bonds $(iv)$ - Unsaturated fatty acid $\rightarrow$ $C=C$ double bonds $(i)$ - Nucleic acid $\rightarrow$ Phosphodiester bonds $(ii)$ - Polysaccharide $\rightarrow$ Glycosidic bonds $(iii)$ Hence, the correct option is **(2)**.