CBSE Class 12 Chemistry Question Paper 2026 with Solutions Set 3

CBSE CLASS XII Questions

• 1.

  What is meant by lanthanoid contraction? (ii) Why do transition metals form coloured compounds? (iii) Why are $E^\circ_{M^{2+}/M}$ values for Mn and Zn more negative than expected? (iv) Which is the most stable oxidation state of Cu and why? (v) Why is Ce$^{4+}$ in aqueous solution a good oxidising agent?

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• 2.

  The following reactions occur at the anode during the electrolysis of aqueous sodium chloride solution: \[ Cl^-_{(aq)} \rightarrow \frac{1}{2}Cl_2(g)+e^- \qquad E^\circ_{\text{cell}}=1.36\,V \] \[ 2H_2O(l) \rightarrow O_2(g)+4H^+(aq)+4e^- \qquad E^\circ_{\text{cell}}=1.23\,V \] Which reaction is feasible at the anode and why?

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• 3.

  The half-life periods of decomposition of $\mathrm{NH_3}$ for different initial pressures are given below :
  

  

  
  The order of the reaction is :

  • zero order
  • first order
  • 0·5
  • second order
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• 4.

  Half-life (\( t_{1/2} \)) of a first order reaction is 1386 s. The value of rate constant is:

  • \(0.5 \times 10^{-4} \, \text{s}^{-1}\)
    
  • \(5.0 \times 10^{-4} \, \text{s}^{-1}\)
    
  • \(0.5 \times 10^{-5} \, \text{s}^{-1}\)
    
  • \(0.5 \times 10^{-3} \, \text{s}^{-1}\)
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• 5.

  A solution is prepared by dissolving 0.025 g of potassium sulphate in 2 L of water at 27$^\circ$C. Assuming potassium sulphate is completely dissociated, determine its osmotic pressure. Given: \[ R=0.082 \, L\,atm\,K^{-1}mol^{-1} \] \[ \text{Molar mass of }K_2SO_4=174\,g\,mol^{-1} \] (ii) What type of azeotrope will be formed by a solution of acetone and chloroform? Give reason.

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• 6.

  Why is C--O--C bond angle in ethers slightly greater than tetrahedral angle?

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