You are an expert CBSE XII CS Computer Science teacher, examiner, and study material creator.

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SCOPE — READ BEFORE GENERATING ANYTHING
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Today's lecture covers ONE topic only: "Stack concept and operations using list"
Lecture number 42 of 91 | Duration: 35 minutes | Board: CBSE
Chapter: Computational Thinking and Programming – 2

HARD RULE: Every piece of content you generate — notes, examples, questions, tips —
must be directly relevant to "Stack concept and operations using list" only.
DO NOT pull content, examples, or questions from any other topic or chapter.

LECTURE MODE: SUBTOPIC PYQ PRACTICE
- Scope: "Stack concept and operations using list" only.
- Do not reteach the topic from scratch. Use a short recap only when a PYQ needs it.
- Main output must be previous-year-question practice: question analysis, marking points, model answers, common mistakes, and timed strategy.
- Use the 13 real PYQ record(s) provided below as the source of truth. Do not fabricate board years, marks, or questions.

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SECTION 1: LECTURE INFORMATION
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Class: XII CS | Subject: Computer Science | Board: CBSE
Topic: Stack concept and operations using list PYQ part 2
Subtopics to cover today:
- Stack concept and operations using list

Student level: Class XII, CBSE Board, average to above-average students preparing for board exams

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SECTION 2: TEACHER'S REFERENCE NOTES
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Stack concept and operations using list PYQ part 2

PYQ PRACTICE SCOPE: Stack concept and operations using list.
Concept ID: U1_STACK_LIST_OPS.
Use only previous-year questions whose concept_ids include U1_STACK_LIST_OPS.

Teaching ideas: Timed PYQ round, board solution, peer marking, and correction of recurring examiner traps.

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SECTION 3: EXAM FREQUENCY DATA (Year-wise)
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Teaching priority: HIGH
High-yield concepts: Stack concept and operations using list

| Year | Questions | Marks |
|------|-----------|-------|
| 2024 | 4 | 16 |
| 2025 | 6 | 20 |
| 2026 | 3 | 9 |
| **Total** | **13** | **45** |

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SECTION 4: ACTUAL PREVIOUS YEAR QUESTIONS
(Scope: "Stack concept and operations using list" only — 13 questions from board papers)
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PYQ LECTURE RULE: use these questions as the source pool for practice.
- This pool has 13 questions: preserve and discuss ALL 13 actual PYQs in Section 7.
- Do not compress, replace, paraphrase, or skip any actual PYQ.
- Do not create substitute or newly framed questions for this small pool.
- Do not fabricate board years, marks, sections, or questions.


--- 2024 Board Exam (4 questions | 16 marks) ---

Q1. [Short Answer] [3M] [Medium] Section-C
A) You have a stack named BooksStack that contains records of books. Each book record is represented as a list containing book_title, author_name, and publication_year.
Write the following user-defined functions in Python to perform the specified operations on the stack BooksStack:
(I) push_book(BooksStack, new_book): This function takes the stack BooksStack and a new book record new_book as arguments and pushes the new book record onto the stack.
(II) pop_book(BooksStack): This function pops the topmost book record from the stack and returns it. If the stack is already empty, the function should display "Underflow".
(III) peep(BookStack): This function displays the topmost element of the stack without deleting it. If the stack is empty, the function should display 'None'.

Q2. [Programming] [3M] [Medium] Section-C
B) Write the definition of a user-defined function push_even(N) which accepts a list of integers in a parameter N and pushes all those integers which are even from the list N into a Stack named EvenNumbers.
Write function pop_even() to pop the topmost number from the stack and returns it. If the stack is already empty, the function should display "Empty".
Write function Disp_even() to display all elements of the stack without deleting them. If the stack is empty, the function should display 'None'.
For example:
If the integers input into the list VALUES are: [10, 5, 8, 3, 12]
Then the stack EvenNumbers should store: [10, 8, 12]

Q3. [Programming] [5M] [Hard] Section-D
A list contains the details of Employees working in an organization. Write the following user defined functions in Python to perform the given operations:
(i) Push_Employee(EmpList) : To push the details of the employees into the stack EmpStack who are working in Admin department.
(ii) Pop_Employee() : To pop the elements from the stack and display. Also display "Empty" when there are no elements in the stack.

For example:
If the list contains the details as:
['EMP01','Raj','Admin']
['EMP02','Shreya','HR']
['EMP03','Rohan','Admin']
['EMP04','Anita','Admin']
['EMP05','Priya','HR']

The output should be:
Anita
Rohan
Empty

Q4. [Short Answer] [5M] [Hard] Section-D
Write the following Python functions:
(i) push_record(): To push the product details of the products whose price is more than 500 into the stack Record.

(ii) pop_record(): To pop the elements from the stack and display. Also display "No Record" when there are no elements in the stack.

--- 2025 Board Exam (6 questions | 20 marks) ---

Q1. [Programming] [3M] [Medium] Section-C
Write a user defined function in Python Push() which takes a list named DATA as an argument and pushes all elements which contain the substring 'books' (case insensitive) onto the list SBOOKS.

Q2. [Programming] [3M] [Medium] Section-C
Write a user defined function in Python Push() which takes a list named DATA as an argument and pushes all even numbers in the list on to the list EVENLIST.

Q3. [Short Answer] [3M] [Medium] Section-C
(a) A stack named KeyStack contains records of some computer keyboards. Each record is represented as a list containing Make, Keys, Connectivity. The Make and Connectivity are strings, and Keys is an integer. For example, a record in the stack may be ('Hitech', 105, 'USB').
Write the following user-defined functions in Python to perform the specified operations on KeyStack :
(I) push_key(KeyStack, new_key) : This function takes the stack KeyStack and a new record as arguments new_key and pushes this new record onto the stack.
(II) pop_key(KeyStack) : This function pops the topmost record from the stack and returns it. If the stack is already empty, the function should display the message "Underflow".
(III) isEmpty(KeyStack) : This function checks whether the stack is empty. If the stack is empty, the function should return True, otherwise the function should return False.

(II) pop_one(St) : The function should pop an element from the stack St, and return this element. If the stack is empty, then the function should display the message 'Stack Underflow', and return None.
(III) display_all(St) : The function should display all the elements of the stack St, without deleting them. If the stack is empty, the function should display the message 'Empty Stack'.

Q4. [Short Answer] [3M] [Medium] Section-C
(b) Write the following user-defined functions in Python :
(I) push_vowels(S,St) : Here S is a string and St is a list representing a stack. The function should push all the vowels of the string S onto the stack St. For example, if the string S is "Easy Concepts", then the function push_vowels() should push the elements 'E','a','o','e' onto the stack.

(II) pop_one(St) : The function should pop an element from the stack St, and return this element. If the stack is empty, then the function should display the message 'Stack Underflow', and return None.
(III) display_all(St) : The function should display all the elements of the stack St, without deleting them. If the stack is empty, the function should display the message 'Empty Stack'.

Q5. [Programming] [3M] [Medium] Section-C
A list containing records of products as
L = [("Laptop", 90000), ("Mobile", 30000), ("Pen", 50), ("Headphones", 1500)]
Write the following user-defined functions to perform operations on a stack named Product to:
I. Push_element() – To push an item containing the product name and price of products costing more than 50 into the stack.
Output: [('Laptop', 90000), ('Mobile', 30000), ('Headphones', 1500)]
II. Pop_element() – To pop the items from the stack and display them. Also, display "Stack Empty" when there are no elements in the stack.
Output:
('Headphones', 1500)
('Mobile', 30000)
('Laptop', 90000)
Stack Empty

Q6. [Programming] [5M] [Hard] Section-D
A list contains the names of boys who participated in an inter school level swimming competition. Write the following user defined functions in Python to perform given operations:
(i) Push_element(Boys) : To push the names of boys in the stack where the length of the name is more than 5 characters.
(ii) Pop_element() : To pop the elements from the stack and display them. Also display "Stack Empty" when there are no elements in the stack.

For example:
If the list of boys who participated in the competition is :
['Rohit', 'Rahul', 'Rishabh', 'Virat', 'Hardik']
The stack should contain
['Rishabh', 'Hardik']
The output should be displayed as:
Hardik
Rishabh
Stack Empty

--- 2026 Board Exam (3 questions | 9 marks) ---

Q1. [Short Answer] [3M] [Medium] Section-C
(a) A stack named FruitStack, implemented using list, contains records of some fruits. Each record is represented as a dictionary with keys 'Name', 'Origin', 'Price', and 'Expiry'.
A sample record is given here :
{'Name':'Apple', 'Origin':'France', 'Price':120, 'Expiry':'12-08-2025'}
Write the following user-defined functions in Python to perform the specified operations on FruitStack :
(i) push_fruit(FruitStack, Fruit): This function takes the stack FruitStack and a new record Fruit as arguments and pushes the record stored in Fruit onto FruitStack if the Price is less than 100.
(ii) pop_fruit(FruitStack) : This function pops the topmost record from the stack and returns it. If the stack is already empty, the function should display "UNDERFLOW".
(iii) display(FruitStack) : This function displays all the elements of the stack starting from the topmost element. If the stack is empty, the function should display 'EMPTY STACK'.

Q2. [Short Answer] [3M] [Medium] Section-C
(b) Write a Python program to accept 10 integers from the user. If the entered number is a three-digit even integer, push it onto a stack. After all inputs are taken, pop all the three-digit even integers from the stack and display them. For example, if the user enters 12, 31, 320, 457, 6, 92, 924, 220, 1, 218, then the stack should contain :
320, 924, 220, 218
and the output of the program should be :
218 220 924 320

Q3. [Output Prediction] [3M] [Medium] Section-C
(a) Write the output of the following code :
def Exam2026(given) :
    new=[]
    for ch in given[1:-1]:
        if ch.isupper():
            new.reverse()
        elif ch not in new:
            new.append(ch)
        elif ch in new:
            new.pop()
    print(new)
Exam2026("Gold-24Medals")

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===========================================
QUESTION PATTERN BANK (What the board actually asks for THIS topic)
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Scope: ONLY questions for today's lecture topic are listed below.
DO NOT import questions from other topics or chapters.
These are concept-pattern summaries (what TYPE the board asks), not copies of the
actual questions — never reproduce full question text here.

### Concept: Stack concept and operations using list
  Pattern: Output Prediction=1, Programming=6, Short Answer=6 | Marks: 3M=10, 5M=3 | Total: 13 questions
  [Short Answer] [3M] [Medium] × 4
    → Core concept of Stack concept and operations using list
  [Programming] [3M] [Medium] × 3
    → Core concept of Stack concept and operations using list
  [Programming] [5M] [Hard] × 2
    → Output/result interpretation for the current concept
  [Short Answer] [5M] [Hard]
    → Core concept of Stack concept and operations using list
  [Programming] [3M] [Medium]
    → Output/result interpretation for the current concept
  [Short Answer] [3M] [Medium]
    → Output/result interpretation for the current concept
  [Output Prediction] [3M] [Medium]
    → Output/result interpretation for the current concept


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IMPORTANCE ANALYSIS (allocate teaching time by this ranking)
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| Rank | Concept | Score | Times Tested | Total Marks | Recent Years | Priority |
|------|---------|-------|-------------|-------------|--------------|----------|
| 1 | Stack concept and operations using list | 115 | 13 | 45M | 2026, 2025, 2024 | CRITICAL |

CRITICAL concepts → full sub-section + comparison table + 2 worked examples
HIGH concepts     → 1 sub-section + 1 worked example
MEDIUM concepts   → definition + 1 quick example only

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EXAMINER FINGERPRINT — TRAPS TO COVER INTERNALLY
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Use the exam-frequency input and actual previous-year questions to identify traps, marking points, and common mistakes. In this PYQ Practice lecture, actual PYQs may be printed in Section 7 only. Do not print them randomly in concept notes, homework, or unrelated sections.

For this lecture, the generated teaching material must strongly cover these traps:

No static trap list exists yet for "Stack concept and operations using list". Self-generate 4–7 traps from:
- actual question patterns for Stack concept and operations using list
- common wrong assumptions students make about this concept
- output-tracing traps
- syntax-vs-runtime traps
- comparison traps
- order/sequence traps

Important: this list should be treated as dynamic — for lectures with no static trap list, generate traps yourself from the categories above rather than leaving this section thin.
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YOUR TASK — Generate a complete classroom-ready teaching package
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Output format: FULL HTML (print-ready, A4, same format as CBSE study material).
Use the CSS classes below. NO plain Markdown — use HTML elements only.

HTML STRUCTURE TO GENERATE:

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<meta name="viewport" content="width=device-width,initial-scale=1">
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body.bw-mode .def-box, body.bw-mode .key-box, body.bw-mode .example-box,
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<!-- TOC SIDEBAR -->
<nav class="toc-sidebar" aria-label="Table of Contents">
  <h4>&#128214; Contents</h4>
  <!-- TOC links auto-built by JS above -->
</nav>

<!-- MAIN CONTENT -->
<div class="main-content">

Generate these sections in order (all inside the main-content div):

<h1 id="top">Stack concept and operations using list PYQ part 2 — Lecture 42</h1>
<p style="text-align:center;color:#555;font-size:8.5pt;">CBSE | XII CS | Computational Thinking and Programming – 2 | 35 min</p>

<h2 id="s1">1. Learning Objectives</h2>
[3–5 objectives derived from what the PYQs above test — use &lt;ul&gt;&lt;li&gt;]

<h2 id="s2">2. 35-Minute Lecture Flow</h2>
[HTML table: Time | Activity | Teacher Action — include a PYQ discussion and full-coverage slot]

<h2 id="s3">3. Quick Concept Recap</h2>
[Keep this section short. Do NOT reteach the full topic from scratch.
Include only the rules needed to solve the PYQs — i.e. the traps listed in the
EXAMINER FINGERPRINT section above (for this lecture: Stack concept and operations using list).
Use .def-box and .key-box only. Add at most one tiny example if needed.
Do not include long theory, long programming tasks, or unrelated examples.]

<h2 id="s4">4. Examiner Tricks &amp; Common Mistakes</h2>
[One .warn-box per trick from the EXAMINER FINGERPRINT list above (plus mistakes visible in the PYQs) — be specific, give the wrong vs right answer]

<h2 id="s5">5. Board Work Plan</h2>
[Numbered list: exactly what to write on the blackboard, in order]

<h2 id="s6">6. Classroom Practice Questions</h2>
[Modelled on PYQ style. CRITICAL: every answer MUST be inside &lt;details&gt;&lt;summary&gt;▶ View Answer&lt;/summary&gt;...&lt;/details&gt; — never expose the answer directly.

Practice questions must follow the difficulty and mark pattern of the actual PYQ pool.

For this topic:
* 3×1M MCQ
* 5×1M/2M Short Answer
* Include 2×3–5M programming practice (the PYQ pool contains long-answer/programming patterns)
* Include 1 HOTS question (the PYQs reveal a genuine higher-order trap)

Every question must be based on one of the traps from Section 4 (EXAMINER FINGERPRINT).
Every answer must be hidden inside &lt;details&gt;&lt;summary&gt;▶ View Answer&lt;/summary&gt;...&lt;/details&gt;.

MCQ structure:
&lt;div class="mcq-box"&gt;
  &lt;b&gt;Q1.&lt;/b&gt; Question text?&lt;br&gt;
  &lt;ul class="options"&gt;
    &lt;li&gt;a) ...&lt;/li&gt;
    &lt;li&gt;b) ...&lt;/li&gt;
    &lt;li&gt;c) ...&lt;/li&gt;
    &lt;li&gt;d) ...&lt;/li&gt;
  &lt;/ul&gt;
  &lt;details&gt;&lt;summary&gt;▶ View Answer&lt;/summary&gt;
    &lt;ul class="options"&gt;
      &lt;li class="wrong"&gt;a) ... — reason why wrong&lt;/li&gt;
      &lt;li class="correct"&gt;b) ... ✓ — reason why correct&lt;/li&gt;
      ...
    &lt;/ul&gt;
  &lt;/details&gt;
&lt;/div&gt;
(Note: options list shown WITHOUT .correct/.wrong BEFORE the details; INSIDE details show all options with correct/wrong analysis.)

Short-answer structure:
&lt;div class="self-test-box"&gt;&lt;b&gt;Q4.&lt;/b&gt; Question&lt;br&gt;&lt;details&gt;&lt;summary&gt;▶ View Answer&lt;/summary&gt;Full answer&lt;/details&gt;&lt;/div&gt;

Dynamic distribution rule:
* If actual PYQs are only 1M/2M, keep generated practice mostly 1M/2M.
* If actual PYQs include 3M/5M programming, include 3M/5M programming practice.
* Never force HOTS or programming questions when the provided PYQ pool does not support them.]

<h2 id="s7">7. PYQ Discussion / Full Coverage (13 source questions)</h2>
[This source pool has 13 actual PYQs.
PYQ COVERAGE RULE:
  - This pool has 13 PYQs, so include and discuss ALL 13 actual PYQs in Section 7.
  - Do not compress, replace, paraphrase, or skip any actual PYQ in this small pool.
  - Compression is allowed only when the source pool has more than 15 questions.
  - Never fabricate board years, marks, sections, or question text.
For every fully discussed actual PYQ include:
  year · marks · type · full question text · concept tested · model answer inside &lt;details&gt; · common mistake inside &lt;details&gt;
Order questions Easy to Tough; within difficulty, order 1 mark → 2 marks → 3 marks → 4/5 marks.
Use this structure for actual PYQ examples:
  Use this structure for each question:
  &lt;div class="pyq-box"&gt;
    &lt;div class="pyq-meta"&gt;[YEAR] · [X] Marks · [TYPE] · Section-[S]&lt;/div&gt;
    &lt;b&gt;Q.&lt;/b&gt; [full question text — include code if any]&lt;br&gt;&lt;br&gt;
    &lt;b&gt;Concept tested:&lt;/b&gt; [concept name]&lt;br&gt;
    &lt;details&gt;&lt;summary&gt;▶ View Model Answer&lt;/summary&gt;
      &lt;b&gt;Model Answer:&lt;/b&gt; [full answer with code/table as needed, using .kw/.bi/.st token spans in &lt;pre&gt;&lt;code&gt;]&lt;br&gt;
      &lt;b&gt;Common mistake:&lt;/b&gt; [what students get wrong — be specific]
    &lt;/details&gt;
  &lt;/div&gt;
]

<h2 id="s8">8. Student Notes (Copy-ready)</h2>
[Concise notes — every concept from PYQs — in .key-box and .def-box; self-check questions in .self-test-box with &lt;details&gt;&lt;summary&gt;▶ View Answer&lt;/summary&gt;answer&lt;/details&gt;]

<h2 id="s9">9. Homework</h2>
[Homework must follow the actual PYQ pattern for this topic:
- 3×1M MCQ
- 3×1M Short Answer
- 2×2M Short Answer only if useful for recap or trap correction
- Include 2×3–5M programming homework (the PYQ pool contains long-answer/programming patterns)
- Every homework question must map to one trap or pattern from Section 4 / Section 7.
Dynamic rule: if actual PYQs are only 1M/2M, homework stays mostly 1M/2M; if they include 3M/5M
programming, homework may include 3M/5M programming; never force unsupported marks or question types.
EVERY answer must be wrapped in &lt;details&gt;&lt;summary&gt;▶ View Answer&lt;/summary&gt;...&lt;/details&gt; inside .self-test-box or .mcq-box.]

<h2 id="s10">10. Exam Tips</h2>
[5 specific tips as .tip-box — derived from PYQ patterns for THIS topic only]

<h2 id="s11">11. Last-Minute Revision Cards</h2>
&lt;div class="card-grid"&gt;
[One .card per concept: &lt;div class="card-title"&gt;[concept]&lt;/div&gt; + 1 rule + 1 example]
&lt;/div&gt;

</div><!-- end .main-content -->
</body>
</html>

HARD OUTPUT RULES:
- Output ONLY the HTML document starting with &lt;!DOCTYPE html&gt;
- Do NOT wrap in markdown code fences
- Do NOT add explanatory text outside the HTML
- Use ONLY content from "Stack concept and operations using list" — zero content from other topics
- PYQ lecture: include and discuss ALL 13 actual PYQs in Section 7; do not compress, replace, paraphrase, or skip any source question
- Always finish the document completely through &lt;/html&gt;. If the answer is getting long, keep Sections 3 and 7 complete, then compact Sections 8–11 instead of truncating.
- If 15 or fewer PYQs are provided, include ALL actual PYQs in Section 7.
- If more than 15 PYQs are provided, fully discuss the highest-yield 15 and list the rest compactly in Section 7 with concept tested + exam trap.
- ANSWER HIDING (most important for student use):
    * Section 6 MCQs: options listed WITHOUT .correct/.wrong BEFORE details; full analysis only INSIDE &lt;details&gt;
    * Section 6 short/programming/HOTS questions: EVERY answer in &lt;details&gt;&lt;summary&gt;▶ View Answer&lt;/summary&gt;...&lt;/details&gt;
    * Section 8 self-check and Section 9 homework: EVERY answer in &lt;details&gt;&lt;summary&gt;▶ View Answer&lt;/summary&gt;
    * Section 7 PYQ Discussion / Full Coverage: model answer + common mistake inside &lt;details&gt;&lt;summary&gt;▶ View Model Answer&lt;/summary&gt;
    * .pyq-box question text and concept tested stay visible outside &lt;details&gt;; only Model Answer + Common mistake are hidden inside &lt;details&gt;
    * The beforeprint JS already auto-opens all &lt;details&gt; for printing — never skip this feature
- INLINE CODE SIZE RULE:
    * Inline code (function/method names and short snippets relevant to "Stack concept and operations using list") must appear almost the same size as surrounding normal text.
    * Do NOT use fixed 8.5pt size for all &lt;code&gt; elements.
    * Use code { font-size:0.95em; } for inline code.
    * Use pre { font-size:8.5pt; } for block code.
    * Use pre code { font-size:inherit; } so code blocks remain compact.
    * Inline code inside paragraphs, tables, boxes, tips, questions, and answers must not look smaller than nearby text.
- BOX / CLASS USAGE: this is a PYQ lecture, so .pyq-box/.pyq-meta are used as shown in Section 7 above (never in theory lectures).
- All content goes inside &lt;div class="main-content"&gt;
- The &lt;nav class="toc-sidebar"&gt; is already in the template — JS auto-builds TOC links
- Print buttons (.print-bar), including Read Mode, are in the template — DO NOT add them again; they auto-hide on print
- Include the full CSS and JS exactly as given (the CODE CSS already follows the INLINE CODE SIZE RULE above).