50 Most important questions For Board Exam Chemistry

 

Based on the latest CBSE Class 12 Chemistry syllabus for the academic year 2024-25, here are 50 important questions for last-minute revision, each accompanied by a concise answer:

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Unit I: Solutions

1. Define molality.

   • Moles of solute per kilogram of solvent.

2. State Raoult's Law for ideal solutions.

   • The partial vapor pressure of each volatile component in a solution is directly proportional to its mole fraction.

3. What is the Van't Hoff factor (i) for K₄[Fe(CN)₆]?

   • 5

4. Name the colligative property used to determine molar mass from the depression in freezing point.

   • Cryoscopy

5. What causes an elevation in boiling point?

   • Addition of a non-volatile solute to a solvent.

Unit II: Electrochemistry

6. What is the standard electrode potential of a standard hydrogen electrode (SHE)?

   • 0 volts

7. Write the Nernst equation for a cell reaction.

   • E = E° - (RT/nF) lnQ

8. Define molar conductivity.

   • Conductivity of an electrolyte solution divided by its molar concentration.

9. What is the primary electrolyte in a lead-acid battery?

   • Sulfuric acid (H₂SO₄)

10. Name a fuel cell used in spacecraft.

    • Hydrogen-oxygen fuel cell

Unit III: Chemical Kinetics

11. Define the rate of a chemical reaction.

    • Change in concentration of reactants or products per unit time.

12. What is the unit of the rate constant for a first-order reaction?

    • s⁻¹

13. State the Arrhenius equation.

    • k = A e^(-Ea/RT)

14. What does the slope represent in an Arrhenius plot?

    • -Ea/R (negative activation energy over the gas constant)

15. Define activation energy.

    • Minimum energy required for reactants to form products.

Unit IV: d- and f-Block Elements

16. Which element is known as the 'transition metal' with the highest melting point?

    • Tungsten (W)

17. What is lanthanoid contraction?

    • Gradual decrease in the size of lanthanoid ions with increasing atomic number.

18. Name the ore from which potassium dichromate is prepared.

    • Chromite (FeCr₂O₄)

19. What is the common oxidation state of actinoids?

    • +3

20. Which transition metal is used in the manufacture of stainless steel?

    • Chromium (Cr)

Unit V: Coordination Compounds

21. Define a ligand.

    • An ion or molecule that donates a pair of electrons to a central metal atom/ion.

22. What is the coordination number of [Fe(CN)₆]³⁻?

    • 6

23. Name the type of isomerism exhibited by [Co(NH₃)₄Cl₂]⁺.

    • Geometrical isomerism

24. What is the oxidation state of platinum in [PtCl₂(NH₃)₂]?

    • +2

25. State Werner's theory in coordination chemistry.

    • It distinguishes between primary (ionizable) and secondary (non-ionizable) valencies of metals.

Unit VI: Haloalkanes and Haloarenes

26. What is the IUPAC name of CH₃-CH₂-Br?

    • Bromoethane

27. Which halogen compound is known as chloroform?

    • Trichloromethane (CHCl₃)

28. What is the major product of chlorination of benzene?

    • Chlorobenzene

29. Name the effect responsible for the deactivating nature of halogens in electrophilic substitution reactions.

    • -I (negative inductive) effect

30. Which environmental pollutant is known as Freon-12?

    • Dichlorodifluoromethane (CCl₂F₂)

Unit VII: Alcohols, Phenols, and Ethers

31. What is the common name of methanol?

    • Wood alcohol

32. Name the process used for the industrial preparation of ethanol.

    • Fermentation

33. What is the IUPAC name of phenol?

    • Benzenol

34. Which reagent is used to oxidize primary alcohols to aldehydes?

    • Pyridinium chlorochromate (PCC)

35. Name the product formed when phenol reacts with bromine water.

    • 2,4,6-Tribromophenol

Unit VIII: Aldehydes, Ketones, and Carboxylic Acids

36. What is the functional group of aldehydes?

    • -CHO

37. Name the simplest ketone.

    • **Acetone