CBSE Class 12 Chemistry Board Exam 2026: How to Solve Numericals & Graph Questions Easily
The CBSE Class 12th Chemistry board exam is on 28 February 2026, conducted by the Central Board of Secondary Education. Compared to theory, numerical and graph-based questions are more scoring because marks are awarded for each step of the solution. Even if a student solves only part of a question, teachers usually give partial marks, so no question should be left unanswered. By following a simple and structured strategy, students can attempt every question confidently and achieve a better score in the exam.
30 Most Expected Questions for CBSE Class 12 Chemistry Exam 2026
How to Solve CBSE Class 12 Chemistry Numerical Problems
A systematic, five-step approach is crucial for solving numerical problems and maximizing marks, especially for securing partial credit. For a typical three-mark question, marks are distributed across these essential steps:
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Identify and List 'Given' Information (0.5 Marks)
Read the question carefully, at least twice. Write down all provided values and conditions. Correctly identifying this information secures the first 0.5 marks. -
Write the Correct 'Formula' (0.5 Marks)
Based on the given data, determine the relevant formula. Simply writing the correct formula earns another 0.5 marks, even if calculations are not completed. -
Perform the 'Calculation' (1.0 Mark)
Substitute the given values into the formula. Show all calculation steps clearly. A correct and well-presented calculation is worth one full mark. -
State the Final 'Answer' (0.5 Marks)
The correct numerical result of your calculation earns 0.5 marks. Even if the final answer is wrong, marks from previous steps can still be secured. -
Include the Correct 'Unit' (0.5 Marks)
The final step is to write the correct unit alongside your answer. This completes the solution and secures the final 0.5 marks.
This step-by-step method ensures you receive partial credit for numerical questions. Never leave a numerical question completely blank.
Applying the 5-Step Method
Consider a question: "At 25°C, the vapor pressure of pure water is given. Calculate the vapor pressure of a 5% aqueous solution of urea." (Molar mass of urea = 60 g/mol, water = 18 g/mol).
Here’s how to break down the solution:
Given (0.5 Marks):
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Pure solvent (water) is 'A'; Solute (urea) is 'B'.
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Vapor pressure of pure water (P°ₐ) is known.
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Goal: Find vapor pressure of solution (Pₛ).
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For a 5% solution: Mass of urea (Wₑ) = 5g, Mass of water (Wₐ) = 95g.
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Molar mass of urea (Mₑ) = 60 g/mol.
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Molar mass of water (Mₐ) = 18 g/mol.
Formula (0.5 Marks):
The relevant principle is the relative lowering of vapor pressure.
Formula: (P°ₐ - Pₛ) / P°ₐ = Xₑ (Mole fraction of solute)
Calculation (1.0 Mark):
Substitute the known values into the formula and solve for Pₛ.
Answer (0.5 Marks):
State the final calculated value of Pₛ.
Unit (0.5 Marks):
Specify the appropriate unit of pressure (e.g., mm Hg, atm).
Important Formulas for Chemistry Numericals
Memorizing key formulas is essential for solving numerical problems. While a list of critical formulas (often marked with a star*) is provided in study materials, memorization alone is insufficient. It is crucial to understand what each variable in a formula represents.
For example, in the formula for Depression in Freezing Point:
ΔTբ = Tբ(solvent) - Tբ(solution) = Kբ × m
You must know that:
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ΔTբ represents the depression in freezing point.
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The freezing point of the pure solvent is higher than that of the solution.
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Kբ is the cryoscopic constant.
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'm' is the molality of the solution.
Understanding these details helps in identifying which formula to apply based on the information given in a problem. (Just as playing a video game like PUBG doesn't make someone a real soldier, simply memorizing formulas doesn't make you proficient at solving numericals. You must engage in active practice and solve a wide variety of problems to build true competence.)
How to Solve Chemistry Graph-Based Questions
Graph-based questions in physical chemistry primarily appear in two formats. Successfully solving either type depends on a strong understanding of the underlying formulas.
Types of Graph Questions
| How to Solve Graph-Based Questions | |||
|---|---|---|---|
| Type | Description | Example | Solution |
| 1. Interpreting a Given Graph | You are provided with a plotted graph and asked to interpret it or answer questions based on its features. | A graph shows that the rate of reaction is constant and does not change with the concentration of the reactant. What is the order of the reaction? | This represents a zero-order reaction. The formula is Rate = k[Reactant]⁰. Since any value raised to the power of zero is 1, the rate equals the constant 'k' and is independent of concentration. |
| 2. Drawing a Graph | You are asked to draw a graph illustrating a specific relationship based on given conditions. This requires knowing the mathematical relationship between the variables. | Draw a graph of Rate vs. Reactant Concentration for a zero-order reaction. | Knowing the formula Rate = k (a constant), you would draw a straight line parallel to the concentration axis, showing that the rate does not change as concentration changes. |
In both scenarios, the formula is the key to the solution. For more complex graphs, the formula helps identify the slope and intercept. By relating the graph's axes (y and x) to the equation of a straight line (y = mx + c), you can determine which part of the formula corresponds to the slope (m) and which to the intercept (c). A list of all important graphs and their corresponding formulas should be reviewed, as at least one of these is highly likely to appear in the exam.
Benefits To Solve Numericals & Graph Questions Easily
A systematic step-by-step method to solve numericals
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How to analyse and interpret chemistry graphs accurately
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Proper formula application and unit management
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Common mistakes students make in board examinations
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Effective answer presentation techniques
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Time management strategy for numerical sections