CBSE Class 12 Chemistry Expected Question Paper 2025

Some Basic Concepts of Chemistry

• What is the symbol for the SI unit of the mole? How is the mole defined?
• 45.4 L of dinitrogen reacted with 22.7 L of dioxygen and 45.4 L of nitrous oxide was formed. 2N2(g) + O2(g) → 2N2O(g). Which law is being obeyed in this experiment? Write the statement of the law.
• What will be the mass of one atom of C-12 in grams?
• A vessel contains 1.6 g of dioxygen at STP (273.15K, 1 atm pressure). The gas is now transferred to another vessel at a constant temperature, where pressure becomes half of the original pressure. Calculate (i) volume of the new vessel. (ii) number of molecules of dioxygen.

Structure of Atom

• Nickel atom can lose two electrons to form Ni²+ ion. The atomic number of nickel is 28. From which orbital will nickel lose two electrons?
• Calculate the total number of angular nodes and radial nodes present in the 3p orbital.
• Which of the following will not show deflection from the path on passing through an electric field? Proton, cathode rays, electron, neutron.
• An atom having atomic mass number 13 has 7 neutrons. What is the atomic number of the atom?

Classification of Elements and Periodicity in Properties

• Explain why the electron gain enthalpy of fluorine is less negative than that of chlorine.
• Identify the group and valency of the element having atomic number 119. Also, predict the outermost electronic configuration and write the general formula of its oxide.
• Among the elements B, Al, C and Si, (i) which element has the highest first ionisation enthalpy? (ii) which element has the most metallic character? Justify your answer in each case.

Chemical Bonding and Molecular Structure

• Explain the non linear shape of H2S and non planar shape of PCl3 using valence shell electron pair repulsion theory.
• Using molecular orbital theory, compare the bond energy and magnetic character of O2+ and O2– species.
• Why does type of overlap given in the following figure not result in bond formation?

State of Matter

• If 1 gram of each of the following gases are taken at ST P, which of the gases will occupy (a) greatest volume and (b) smallest volume? CO, H2O, CH4, NO
• The behaviour of matter in different states is governed by various physical laws. According to you what are the factors that determine the state of matter?

Chemical Thermodynamics

• One mole of acetone requires less heat to vapourise than 1 mol of water. Which of the two liquids has a higher enthalpy of vapourisatIon?
• Given that ΔH = 0 for mixing of two gases. Explain whether the diffusion of these gases into each other in a closed container is a spontaneous process or not?
• Increase In enthalpy of the surroundings is equal to decrease In enthalpy of the system. Will the temperature of system and surroundings be the same when they are In thermal equilibrium?

Equilibrium

• BF3 does not have protons but still acts as an acid and reacts with NH3. Why is it so? What type of bond is formed between the two?
• The pH of a solution of a strong acid is 5.0. What will be the pH of the solution obtained after diluting the given solution 100 times?

Redox Reactions

• Explain redox reactions on the basis of electron transfer. Give suitable examples.
• Why does fluorine not show a disproportionation reaction?

P & S Block Elements

• How do you account for the strong reducing power of lithium in aqueous solution?
• Draw the structure of boric acid showing hydrogen bonding. Which species is present in water? What is the hybridisation of boron in this species?
• When heated in air, the alkali metals form various oxides. Mention the oxides formed by Li, Na, and K.
• The +1 oxidation state in group 13 and +2 oxidation state in group 14 becomes more and more stable with increasing atomic number. Explain.