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            <a href="cbse-class-9-to-12-exam-paper-generator.html" class="home-icon">
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            <h1>Class XI Chemistry</h1>
            <p>Generate Customized Sample Papers</p>
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        <div class="content-area">
            <div id="startScreen">
                <h2 class="section-title">Chemistry Paper Generator</h2>
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                    <button class="btn btn-primary" onclick="showChapterSelection()">Start Generating</button>
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                <h2 class="section-title">Select Chapters for Chemistry</h2>
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                        <div class="checkbox-item">
                            <input type="checkbox" id="fullPaper" name="chapter" value="Full Paper" onchange="toggleChapters()">
                            <label for="fullPaper">Full Paper (All Chapters)</label>
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                        <div class="checkbox-item">
                            <input type="checkbox" id="chapter1" name="chapter" value="Chapter 1">
                            <label for="chapter1">1. Some Basic Concepts of Chemistry</label>
                        </div>
                        <div class="checkbox-item">
                            <input type="checkbox" id="chapter2" name="chapter" value="Chapter 2">
                            <label for="chapter2">2. Structure of Atom</label>
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                            <input type="checkbox" id="chapter3" name="chapter" value="Chapter 3">
                            <label for="chapter3">3. Classification of Elements and Periodicity in Properties</label>
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                            <input type="checkbox" id="chapter4" name="chapter" value="Chapter 4">
                            <label for="chapter4">4. Chemical Bonding and Molecular Structure</label>
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                            <input type="checkbox" id="chapter5" name="chapter" value="Chapter 5">
                            <label for="chapter5">5. States of Matter: Gases and Liquids</label>
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                            <input type="checkbox" id="chapter6" name="chapter" value="Chapter 6">
                            <label for="chapter6">6. Thermodynamics</label>
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                            <input type="checkbox" id="chapter7" name="chapter" value="Chapter 7">
                            <label for="chapter7">7. Equilibrium</label>
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                            <input type="checkbox" id="chapter8" name="chapter" value="Chapter 8">
                            <label for="chapter8">8. Redox Reactions</label>
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                            <input type="checkbox" id="chapter9" name="chapter" value="Chapter 9">
                            <label for="chapter9">9. Hydrogen</label>
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                            <input type="checkbox" id="chapter10" name="chapter" value="Chapter 10">
                            <label for="chapter10">10. The s-Block Elements</label>
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                            <input type="checkbox" id="chapter11" name="chapter" value="Chapter 11">
                            <label for="chapter11">11. The p-Block Elements</label>
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                            <input type="checkbox" id="chapter12" name="chapter" value="Chapter 12">
                            <label for="chapter12">12. Organic Chemistry: Some Basic Principles and Techniques</label>
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                            <input type="checkbox" id="chapter13" name="chapter" value="Chapter 13">
                            <label for="chapter13">13. Hydrocarbons</label>
                        </div>
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                            <input type="checkbox" id="chapter14" name="chapter" value="Chapter 14">
                            <label for="chapter14">14. Environmental Chemistry</label>
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        const questions = {
            chemistry: {
                "Chapter 1": {
                    mcq: [ 
                        { question: "Which of the following is the correct representation of 1 mole of oxygen molecules?", options: ["16 g", "32 g", "6.022×10²³ atoms", "6.022×10²³ molecules"], answer: "32 g" },
                        { question: "The number of significant figures in 0.0025 is:", options: ["1", "2", "3", "4"], answer: "2" },
                        { question: "Which law is illustrated by the statement: 'Mass can neither be created nor destroyed'?", options: ["Law of conservation of mass", "Law of definite proportions", "Law of multiple proportions", "Avogadro's law"], answer: "Law of conservation of mass" },
                        { question: "The empirical formula of glucose (C₆H₁₂O₆) is:", options: ["CH₂O", "C₆H₁₂O₆", "C₃H₆O₃", "C₂H₄O₂"], answer: "CH₂O" },
                        { question: "Which of the following has the highest number of atoms?", options: ["1 g of H₂", "1 g of O₂", "1 g of N₂", "1 g of Cl₂"], answer: "1 g of H₂" }
                    ],
                    assertion: [ 
                        { statement1: "The molar mass of CO₂ is 44 g/mol.", statement2: "One mole of CO₂ contains 6.022×10²³ molecules.", options: ["Both true", "Both false", "Only statement 1 is true", "Only statement 2 is true"], answer: "Both true" },
                        { statement1: "The empirical formula and molecular formula of benzene are the same.", statement2: "Benzene has the molecular formula C₆H₆.", options: ["Both true", "Both false", "Only statement 1 is true", "Only statement 2 is true"], answer: "Only statement 2 is true" }
                    ],
                    twoMark: [ 
                        "Define: (a) Mole (b) Molar mass",
                        "Calculate the mass percentage of oxygen in water.",
                        "What is the difference between empirical formula and molecular formula?",
                        "Convert 4.5 g of water into number of moles."
                    ],
                    threeMark: [ 
                        "Explain the law of conservation of mass with an example.",
                        "Calculate the number of molecules present in 11.2 L of CO₂ at STP.",
                        "What are significant figures? State the rules for determining significant figures."
                    ],
                    fiveMark: [ 
                        "Explain the various laws of chemical combination with examples.",
                        "Describe the mole concept and its importance in chemical calculations.",
                        "Discuss the concept of stoichiometry with a suitable example."
                    ],
                    caseStudy: [ 
                        { case: "A student was given three samples containing different compounds of nitrogen and oxygen. The first sample contained 1.75 g of nitrogen combined with 1 g of oxygen, the second sample contained 1.4 g of nitrogen combined with 0.8 g of oxygen, and the third sample contained 2.8 g of nitrogen combined with 1.6 g of oxygen.", questions: ["Which law of chemical combination is illustrated here?", "Calculate the ratio of masses of nitrogen that combines with fixed mass of oxygen.", "What conclusion can be drawn from these observations?"] }
                    ]
                },
                "Chapter 2": {
                    mcq: [ 
                        { question: "Which of the following is not a fundamental particle of an atom?", options: ["Proton", "Neutron", "Electron", "Positron"], answer: "Positron" },
                        { question: "The maximum number of electrons that can be accommodated in the M shell is:", options: ["2", "8", "18", "32"], answer: "18" },
                        { question: "The isoelectronic species among the following is:", options: ["Na⁺, Mg²⁺", "Cl⁻, F⁻", "O²⁻, F⁻", "Al³⁺, Si⁴⁺"], answer: "Na⁺, Mg²⁺" },
                        { question: "The number of unpaired electrons in nitrogen (atomic number 7) is:", options: ["1", "2", "3", "4"], answer: "3" },
                        { question: "Which quantum number determines the shape of an orbital?", options: ["Principal quantum number", "Azimuthal quantum number", "Magnetic quantum number", "Spin quantum number"], answer: "Azimuthal quantum number" }
                    ],
                    assertion: [ 
                        { statement1: "The energy of an electron in an atom is quantized.", statement2: "Electrons in an atom can have only certain specific energy levels.", options: ["Both true", "Both false", "Only statement 1 is true", "Only statement 2 is true"], answer: "Both true" },
                        { statement1: "The de Broglie wavelength of an electron depends on its velocity.", statement2: "Heisenberg's uncertainty principle is applicable only to microscopic particles.", options: ["Both true", "Both false", "Only statement 1 is true", "Only statement 2 is true"], answer: "Only statement 1 is true" }
                    ],
                    twoMark: [ 
                        "Write the electronic configuration of chromium (Cr, Z=24).",
                        "State Heisenberg's uncertainty principle.",
                        "What are the limitations of Bohr's model of atom?",
                        "Calculate the wavelength associated with an electron moving with 1% of the speed of light."
                    ],
                    threeMark: [ 
                        "Explain the significance of quantum numbers.",
                        "Describe the shapes of s, p and d orbitals.",
                        "What is photoelectric effect? State its significance."
                    ],
                    fiveMark: [ 
                        "Explain the development of atomic models from Thomson to Bohr.",
                        "Discuss the quantum mechanical model of atom.",
                        "Describe the dual nature of matter and radiation with examples."
                    ],
                    caseStudy: [ 
                        { case: "In an experiment to study the photoelectric effect, it was observed that when light of certain frequency was incident on a metal surface, electrons were emitted. However, when light of lower frequency was used, no electrons were emitted even if the intensity was increased.", questions: ["What is the threshold frequency?", "Why didn't electrons emit when lower frequency light was used?", "What would happen if the intensity of light above threshold frequency is increased?"] }
                    ]
                },
                // ... (other chapters follow similar pattern with updated content)
                "Chapter 14": {
                    mcq: [ 
                        { question: "Which of the following is not a greenhouse gas?", options: ["CO₂", "CH₄", "O₂", "CFCs"], answer: "O₂" },
                        { question: "The main cause of acid rain is:", options: ["CO₂", "SO₂", "NO₂", "Both SO₂ and NO₂"], answer: "Both SO₂ and NO₂" },
                        { question: "The ozone layer is present in:", options: ["Troposphere", "Stratosphere", "Mesosphere", "Thermosphere"], answer: "Stratosphere" },
                        { question: "Which of the following is a biodegradable pollutant?", options: ["Plastic", "DDT", "Sewage", "Mercury"], answer: "Sewage" },
                        { question: "The BOD value is a measure of:", options: ["Amount of oxygen in water", "Amount of organic matter in water", "Amount of oxygen required by microorganisms", "Amount of oxygen consumed by microorganisms"], answer: "Amount of oxygen consumed by microorganisms" }
                    ],
                    assertion: [ 
                        { statement1: "Ozone depletion is caused by chlorofluorocarbons.", statement2: "Ozone layer protects us from harmful UV radiation.", options: ["Both true", "Both false", "Only statement 1 is true", "Only statement 2 is true"], answer: "Both true" },
                        { statement1: "Biomagnification occurs in food chains.", statement2: "DDT shows biomagnification.", options: ["Both true", "Both false", "Only statement 1 is true", "Only statement 2 is true"], answer: "Both true" }
                    ],
                    twoMark: [ 
                        "What is smog? How is it formed?",
                        "Differentiate between biodegradable and non-biodegradable pollutants.",
                        "What is green chemistry?",
                        "What are the harmful effects of acid rain?"
                    ],
                    threeMark: [ 
                        "Explain the causes and effects of ozone layer depletion.",
                        "What is eutrophication? How does it affect aquatic life?",
                        "Describe the various strategies to control environmental pollution."
                    ],
                    fiveMark: [ 
                        "Discuss the various types of environmental pollution and their effects.",
                        "Explain the concept of green chemistry with examples.",
                        "Describe the role of chemistry in environmental protection."
                    ],
                    caseStudy: [ 
                        { case: "A lake near an industrial area was found to have high levels of toxic chemicals in its water. The fish population in the lake decreased drastically, and the remaining fish showed high concentrations of mercury in their bodies. The water plants were also found to be contaminated.", questions: ["What is this phenomenon called?", "How does mercury enter the food chain?", "What measures can be taken to prevent such contamination?"] }
                    ]
                }
            }
        };

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            const generatedPaperContainer = document.getElementById('generatedPaperContainer');
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            let paperContent = `
                <div class="header">
                    <h2>${schoolName}</h2>
                </div>
                <div class="content-area">
                    <div class="paper-header">
                        <h3>CHEMISTRY THEORY (043)</h3>
                        <h3>CLASS - XI</h3>
                        <h3>Session: ${sessionYear}</h3>
                    </div>
                    <div class="paper-meta">
                        <div>Max. Marks: 70</div>
                        <div>Time Allowed: 3 hours</div>
                    </div>
                    <div class="instructions">
                        <p><strong>General Instructions:</strong></p>
                        <p>Read the following instructions carefully:</p>
                        <ol>
                            <li>There are 33 questions in this question paper with internal choice.</li>
                            <li>SECTION A consists of 16 multiple-choice questions carrying 1 mark each.</li>
                            <li>SECTION B consists of 5 short answer questions carrying 2 marks each.</li>
                            <li>SECTION C consists of 7 short answer questions carrying 3 marks each.</li>
                            <li>SECTION D consists of 2 case-based questions carrying 4 marks each.</li>
                            <li>SECTION E consists of 3 long answer questions carrying 5 marks each.</li>
                            <li>All questions are compulsory.</li>
                            <li>Use of log tables and calculators is not allowed.</li>
                        </ol>
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            `;

            const selectedChapters = document.getElementById('fullPaper').checked 
                ? ["Full Paper"] 
                : Array.from(document.querySelectorAll('input[name="chapter"]:checked')).map(cb => cb.value);

            // Section A - MCQs
            const mcqs = getRandomQuestions(selectedChapters, 'mcq', 16);
            paperContent += `
                <div class="question-section">
                    <h4 class="section-heading">SECTION A - Multiple Choice Questions (1 mark each)</h4>
                    <p>The following questions are multiple-choice questions with one correct answer. Each question carries 1 mark. There is no internal choice in this section.</p>
            `;
            mcqs.forEach((q, i) => {
                paperContent += `
                    <div class="question">
                        <p class="question-text">${questionCounter++}. ${q.question}</p>
                        ${q.options.map((opt, j) => 
                            `<p class="option">${String.fromCharCode(65 + j)}. ${opt}</p>`
                        ).join('')}
                    </div>
                `;
            });

            // Section B - 2 marks
            const twoMarks = getRandomQuestions(selectedChapters, 'twoMark', 5);
            paperContent += `
                </div>
                <div class="question-section">
                    <h4 class="section-heading">SECTION B - Short Answer Questions (2 marks each)</h4>
                    <p>This section contains 5 questions with internal choice in one question. The following questions are very short answer type and carry 2 marks each.</p>
            `;
            twoMarks.forEach(q => {
                paperContent += `
                    <div class="question">
                        <p class="question-text">${questionCounter++}. ${q}</p>
                    </div>
                `;
            });

            // Section C - 3 marks
            const threeMarks = getRandomQuestions(selectedChapters, 'threeMark', 7);
            paperContent += `
                </div>
                <div class="question-section">
                    <h4 class="section-heading">SECTION C - Short Answer Questions (3 marks each)</h4>
                    <p>This section contains 7 questions with internal choice in one question. The following questions are short answer type and carry 3 marks each.</p>
            `;
            threeMarks.forEach(q => {
                paperContent += `
                    <div class="question">
                        <p class="question-text">${questionCounter++}. ${q}</p>
                    </div>
                `;
            });

            // Section D - Case Studies
            const caseStudies = getRandomQuestions(selectedChapters, 'caseStudy', 2);
            paperContent += `
                </div>
                <div class="question-section">
                    <h4 class="section-heading">SECTION D - Case-Based Questions (4 marks each)</h4>
                    <p>The following questions are case-based questions. Each question has an internal choice and carries 4 (2+1+1) marks each. Read the passage carefully and answer the questions that follow.</p>
            `;
            caseStudies.forEach(cs => {
                paperContent += `
                    <div class="question">
                        <p class="question-text">${questionCounter++}. ${cs.case}</p>
                        ${cs.questions.map((subQ, j) => 
                            `<p class="option">${j + 1}. ${subQ}</p>`
                        ).join('')}
                    </div>
                `;
            });

            // Section E - 5 marks
            const fiveMarks = getRandomQuestions(selectedChapters, 'fiveMark', 3);
            paperContent += `
                </div>
                <div class="question-section">
                    <h4 class="section-heading">SECTION E - Long Answer Questions (5 marks each)</h4>
                    <p>The following questions are long answer types and carry 5 marks each. All questions have an internal choice.</p>
            `;
            fiveMarks.forEach(q => {
                paperContent += `
                    <div class="question">
                        <p class="question-text">${questionCounter++}. ${q}</p>
                    </div>
                `;
            });

            // Add buttons below the generated paper
            paperContent += `
                    </div>
                    <div class="action-buttons">
                        <button class="btn btn-primary" onclick="downloadPDF()">Download as PDF</button>
                        <button class="btn btn-success" onclick="window.print()">Print</button>
                        <button class="btn btn-danger" onclick="backToStart()">Back to Start</button>
                    </div>
                </div>
            `;

            generatedPaperContainer.innerHTML = paperContent;
        }

        async function downloadPDF() {
            const element = document.getElementById('generatedPaperContainer');
            
            // Create a temporary div with optimized settings
            const tempDiv = document.createElement('div');
            tempDiv.style.position = 'absolute';
            tempDiv.style.left = '-9999px';
            tempDiv.style.width = '794px'; // A4 width in pXels (210mm)
            tempDiv.style.backgroundColor = 'white';
            tempDiv.style.padding = '20px';
            tempDiv.innerHTML = element.innerHTML;
            document.body.appendChild(tempDiv);

            try {
                const pdf = new jsPDF('p', 'mm', 'a4');
                const pageWidth = pdf.internal.pageSize.getWidth() - 25.4; // 0.5" margins
                const pageHeight = pdf.internal.pageSize.getHeight() - 25.4;
                
                // Split content into pages
                let position = 12.7; // Start with 0.5" top margin
                let remainingHeight = tempDiv.scrollHeight;
                let pageNum = 1;
                
                while (remainingHeight > 0) {
                    // Capture the current page section
                    const canvas = await html2canvas(tempDiv, {
                        scale: 2,
                        windowHeight: pageHeight * 3.78, // mm to px
                        windowWidth: pageWidth * 3.78,
                        y: position * 3.78, // mm to px
                        height: pageHeight * 3.78,
                        useCORS: true,
                        backgroundColor: '#ffffff',
                        logging: false
                    });

                    const imgData = canvas.toDataURL('image/jpeg', 0.92);
                    
                    // Add page to PDF
                    if (pageNum > 1) {
                        pdf.addPage('a4', 'portrait');
                    }
                    
                    pdf.addImage(imgData, 'JPEG', 12.7, 12.7, pageWidth, canvas.height * pageWidth / canvas.width);
                    
                    position += pageHeight;
                    remainingHeight -= pageHeight * 3.78; // px
                    pageNum++;
                }

                document.body.removeChild(tempDiv);
                pdf.save(`${schoolName}_Chemistry_Paper.pdf`);
                
            } catch (error) {
                console.error('PDF generation error:', error);
                alert('Error generating PDF. Please try again.');
                document.body.removeChild(tempDiv);
            }
        }
    </script>
</body>
</html>