OMTEX AD 2

HSC 12th Important Board Question Paper 2026 Chemistry (Maharashtra Board) | Target 90+ Marks

HSC CHEMISTRY BOARD EXAM 2026 - IMPORTANT PAPER

General Instructions:
  • The question paper is divided into four sections: Section A, B, C, and D.
  • Section A: Q.1 contains 10 MCQs (1 mark each); Q.2 contains 8 Very Short Answers (1 mark each).
  • Section B: Q.3 to Q.14 are 12 Short Answers-I (Attempt any 8, 2 marks each).
  • Section C: Q.15 to Q.26 are 12 Short Answers-II (Attempt any 8, 3 marks each).
  • Section D: Q.27 to Q.31 are 5 Long Answers (Attempt any 3, 4 marks each).
  • Use of log tables is allowed. Calculators are prohibited.
Note: This is a Model Question Paper for the 2026 Board Examination, based on the latest pattern.
Section A
Q.1 Select and write the correct answer for the following multiple choice type of questions:
(i) Integrated rate law equation for a zero order reaction is -
(a) $Kt = [A]_0 - [A]_t$
(b) $Kt = 2.303 \log_{10}\frac{[A]_0}{[A]_t}$
(c) $K = \frac{[A]_t - [A]_0}{t}$
(d) $Kt = 2.303 \log_{10}\frac{[A]_t}{[A]_0}$
Answer: (a) $Kt = [A]_0 - [A]_t$
(ii) The spin only magnetic moment of $Fe^{2+}$ ion is (At. No. Fe = 26) -
(a) 3.806 BM (b) 4.899 BM (c) 5.796 BM (d) 6.817 BM
Answer: (b) 4.899 BM
Explanation: $Fe^{2+}$ has 4 unpaired electrons ($3d^6$). $\mu = \sqrt{n(n+2)} = \sqrt{4(6)} = \sqrt{24} \approx 4.899$ BM.
(iii) The monomer used in the preparation of thermocol is -
(a) vinyl chloride (b) acrylamide (c) butadiene (d) styrene
Answer: (d) styrene
(iv) The pH of 0.01M solution of HCl is -
(a) 4 (b) 3 (c) 2 (d) 1
Answer: (c) 2
Explanation: $pH = -\log[H^+] = -\log(10^{-2}) = 2$.
(v) Which of the following $\alpha$-amino acids does not contain a chiral centre?
(a) alanine (b) valine (c) leucine (d) glycine
Answer: (d) glycine
(vi) Schottky defect is NOT observed in:
(a) NaCl (b) KCl (c) AgBr (d) NiO
Answer: (d) NiO
(vii) Coordination number of atoms in bcc crystal lattice is:
(a) 2 (b) 4 (c) 6 (d) 8
Answer: (d) 8
(viii) The metal used in preparation of Grignard reagent is:
(a) Al (b) Mg (c) Na (d) Fe
Answer: (b) Mg
(ix) The reaction used to convert toluene to benzaldehyde is known as:
(a) Etard's reaction (b) Gatterman-Koch reaction (c) Friedel-Crafts reaction (d) Swartz reaction
Answer: (a) Etard's reaction
(x) A better reagent to convert primary alcohol to aldehyde is:
(a) $KMnO_4$ (b) Pyridinium chlorochromate (PCC) (c) $K_2Cr_2O_7$ (d) Chromic anhydride
Answer: (b) Pyridinium chlorochromate
Q.2 Answer the following questions:

(i) Write the electronic configuration of $Zn^{2+}$ ion (Atomic number = 30).

Answer: $[Ar] 3d^{10}$

(ii) Write the IUPAC name of $Na_3[AlF_6]$.

Answer: Sodium hexafluoroaluminate(III)

(iii) Write the name of insecticide used instead of DDT.

Answer: BHC (Benzene Hexachloride) or Lindane.

(iv) What is the effect of increase in concentration of 'A' on rate of reaction if order $x < 0$?

Answer: The rate of reaction will decrease.

(v) Write the condition for spontaneity of reaction with respect to entropy.

Answer: $\Delta S_{total} > 0$ (Total entropy of system and surroundings must increase).

(vi) Write the SI unit of molar conductivity.

Answer: $S \, m^2 \, mol^{-1}$ or $\Omega^{-1} \, cm^2 \, mol^{-1}$.

(vii) Write the number of donor atoms present in EDTA.

Answer: Six (Hexadentate ligand).

(viii) Write the monomer used for preparation of PVC.

Answer: Vinyl chloride (Chloroethene).
Section B (Attempt any Eight)

Q.3 Differentiate between ionic crystals and covalent crystals.

Ionic CrystalsCovalent Crystals
Constituent particles are ions.Constituent particles are atoms.
Held by electrostatic forces.Held by covalent bonds.
Hard but brittle.Very hard and rigid.

Q.4 Deduce first law of thermodynamics for isothermal and isochoric processes.

Isothermal ($\Delta U = 0$): $Q = -W$. Heat absorbed equals work done by the system.
Isochoric ($W = 0$): $\Delta U = Q_v$. Internal energy change equals heat exchanged at constant volume.

Q.5 Define Buffer solution. Write Henderson-Hasselbalch equation for acidic buffer.

Buffer: A solution that resists changes in pH upon addition of small amounts of acid or base.
Equation: $pH = pK_a + \log_{10} \frac{[Salt]}{[Acid]}$

Q.6 Write the preparation of Nylon-6 and its two uses.

Preparation: Ring-opening polymerization of $\epsilon$-caprolactam at high temperature with water.
Uses: 1. Making tyre cords. 2. Making ropes and fabrics.

Q.7 Calculate the standard potential of the cell: $Zn | Zn^{2+} || Cr^{3+} | Cr$. Given $E^0_{Zn} = -0.76V, E^0_{Cr} = -0.74V$.

$E^0_{cell} = E^0_{cathode} - E^0_{anode} = (-0.74) - (-0.76) = +0.02V$.

Q.8 Define: (a) Pyrometallurgy (b) Roasting.

(a) Pyrometallurgy: Process of extracting metals by heating the ore with a reducing agent at high temperatures.
(b) Roasting: Heating ore in regular supply of air below its melting point to convert sulfides to oxides.

Q.9 Explain anomalous behaviour of oxygen with respect to atomicity and magnetic property.

Atomicity: Oxygen is diatomic ($O_2$), others in group are polyatomic ($S_8$).
Magnetic Property: $O_2$ is paramagnetic, others are diamagnetic.

Q.10 Distinguish between order and molecularity of a reaction.

Order is experimental; molecularity is theoretical. Order can be zero/fractional; molecularity is always a whole number.

Q.11 Write two principles of Green Chemistry.

1. Prevention of waste. 2. Atom economy (maximize incorporation of materials into final product).

Q.12 Write salient features of $SN^1$ mechanism.

Two-step process, formation of carbocation intermediate, first-order kinetics, results in racemization.
Section C (Attempt any Eight)

Q.15 Explain optical isomerism in 2-chlorobutane.

2-chlorobutane contains a chiral carbon. It exists as two non-superimposable mirror images (enantiomers): d-form and l-form. [Include structure of CH3-CH(Cl)-C2H5]

Q.16 Derive Ostwald’s dilution law for a weak acid.

For acid $HA \rightleftharpoons H^+ + A^-$, $K_a = \frac{\alpha^2 C}{1-\alpha}$. For weak acids, $1-\alpha \approx 1$, so $K_a = \alpha^2 C$ or $\alpha = \sqrt{K_a/C}$.

Q.17 Calculate the standard enthalpy of the reaction: $SiO_{2(s)} + 3C_{(graphite)} \rightarrow SiC_{(s)} + 2CO_{(g)}$

Using Hess's Law and given data: $\Delta_r H^0 = \sum \Delta H^0_{products} - \sum \Delta H^0_{reactants}$. [Apply values from source]

Q.18 Explain the formation of $[Co(NH_3)_6]^{3+}$ on the basis of VBT.

$Co^{3+}$: $3d^6$. $NH_3$ is a strong field ligand, causes pairing. Hybridization: $d^2sp^3$ (Inner orbital complex). Geometry: Octahedral. Magnetic property: Diamagnetic.

Q.19 60% of a reactant decomposes in 45 minutes in a first-order reaction. Calculate half-life.

$k = \frac{2.303}{t} \log \frac{100}{100-60} = \frac{2.303}{45} \log(2.5)$. Then, $t_{1/2} = \frac{0.693}{k}$.

Q.20 Write the general electronic configuration of 3d series. Draw structures of sulfuric and thiosulfuric acid.

Configuration: $[Ar] 3d^{1-10} 4s^{1-2}$. [Draw H2SO4 and H2S2O3 structures].

Q.21 Explain Cross Cannizzaro reaction with an example.

Reaction between two different aldehydes (neither having $\alpha$-hydrogen) in presence of strong base. Example: Benzaldehyde + Formaldehyde $\rightarrow$ Benzyl alcohol + Sodium formate.

Q.22 What are nanomaterials? Explain any two applications.

Materials with at least one dimension between 1-100 nm. Applications: 1. Sunscreens (ZnO nanoparticles). 2. Targeted drug delivery in medicine.
Section D (Attempt any Three)

Q.27 (a) How is dioxygen prepared from $KClO_3$? (b) Convert phenol to benzoquinone and cyclohexanol.

(a) $2KClO_3 \xrightarrow{MnO_2, \Delta} 2KCl + 3O_2$.
(b) Phenol + $Na_2Cr_2O_7/H_2SO_4 \rightarrow$ p-Benzoquinone.
Phenol + $H_2/Ni \rightarrow$ Cyclohexanol.

Q.28 Define: Standard enthalpy of combustion and atomization. Draw D-ribose structure and write uses of bronze.

Combustion: Enthalpy change when 1 mole of substance is burnt in excess oxygen.
Atomization: Enthalpy change when 1 mole of gaseous atoms are formed from the element.
Bronze uses: Making statues, medals, and ship propellers.

Q.29 Derive Raoult's law for non-volatile solute. Explain common ion effect.

$P_1 = P^0_1 X_1$. The relative lowering of vapour pressure equals the mole fraction of the solute: $\frac{P^0_1 - P_1}{P^0_1} = X_2$.
Common Ion Effect: Suppression of dissociation of a weak electrolyte by adding a strong electrolyte containing a common ion.

Q.30 Calculate the density of gold (fcc, edge length 408 pm, M = 197 g/mol).

$\rho = \frac{z \cdot M}{a^3 \cdot N_A} = \frac{4 \cdot 197}{(408 \times 10^{-10})^3 \cdot 6.022 \times 10^{23}}$.

Q.31 (a) Explain $SN^2$ mechanism. (b) Convert: Acetic acid to ethyl acetate and ethyl alcohol.

$SN^2$: Single-step, backside attack, inversion of configuration (Walden inversion).
Conversion:
1. $CH_3COOH + C_2H_5OH \xrightarrow{H^+} CH_3COOC_2H_5$ (Esterification).
2. $CH_3COOH \xrightarrow{LiAlH_4} CH_3CH_2OH$.

12th Chemistry with Solution

HSC Chemistry

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