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: "Function definition, call and return"
Lecture number 15 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 "Function definition, call and return" only.
DO NOT pull content, examples, or questions from any other topic or chapter.

LECTURE MODE: SUBTOPIC PYQ PRACTICE
- Scope: "Function definition, call and return" 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 18 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: Function definition, call and return PYQ
Subtopics to cover today:
- Function definition, call and return

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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Function definition, call and return PYQ

PYQ PRACTICE SCOPE: Function definition, call and return.
Concept ID: U1_FUNCTION_DEF_RETURN.
Use only previous-year questions whose concept_ids include U1_FUNCTION_DEF_RETURN.

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: Function definition call and return

| Year | Questions | Marks |
|------|-----------|-------|
| 2021 | 3 | 3 |
| 2022 | 1 | 2 |
| 2023 | 5 | 12 |
| 2024 | 4 | 8 |
| 2025 | 4 | 7 |
| 2026 | 1 | 2 |
| **Total** | **18** | **34** |

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SECTION 4: ACTUAL PREVIOUS YEAR QUESTIONS
(Scope: "Function definition, call and return" only — 18 questions from board papers)
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PYQ LECTURE RULE: use these questions as the source pool for practice.
- Cover every concept tested across the full PYQ pool.
- Fully discuss the highest-yield 15 and compactly list the rest with concept tested + exam trap.
- Compression and representative questions are allowed only for repeated patterns beyond the fully discussed 15.
- Do not fabricate board years, marks, sections, or questions.
- Representative questions must never be labelled as real board questions.


--- 2021 Board Exam (3 questions | 3 marks) ---

Q1. [MCQ] [1M] [Easy] Section-A
Which of the following function header is correct?
a) def cal_si(p=100, r, t=2)
b) def cal_si(p=100, r=8, t)
c) def cal_si(p, r=8, t)
d) def cal_si(p, r=8, t=2)

Q2. [MCQ] [1M] [Easy] Section-A
Which of the following is the correct way to call a function?
a) my_func()
b) def my_func()
c) return my_func
d) call my_func()

Q3. [MCQ] [1M] [Easy] Section-B
What is the output of the following code snippet?
def ChangeVal(M,N):
    for i in range(N):
        if M[i]%5 == 0:
            M[i]//=5
        if M[i]%3 == 0:
            M[i]//=3
L = [25,8,75,12]
ChangeVal(L,4)
for i in L:
    print(i,end="#")
a) 5#8#15#4#
b) 5#8#5#4#
c) 5#8#15#14#
d) 5#18#15#4#

--- 2022 Board Exam (1 question | 2 marks) ---

Q1. [Short Answer] [2M] [Easy] Section-B
Rao has written a code to input a number and check whether it is prime or not. His code is having errors. Rewrite the correct code and underline the corrections made.
def prime():
    n=int(input("Enter number to check :: ")
    for i in range (2, n//2):
        if n%i=0:
            print("Number is not prime \n")
            break
    else:
        print("Number is prime \n')

--- 2023 Board Exam (5 questions | 12 marks) ---

Q1. [Programming] [2M] [Easy] Section-B
Atharva is a Python programmer working on a program to find and return the maximum value from the list. The code written below has syntactical errors. Rewrite the correct code and underline the corrections made.
def max num (L)
max=L (0)
for a in L
if a > max
max=a
return max

Q2. [Programming] [2M] [Easy] Section-B
Ravi, a Python programmer, is working on a project in which he wants to write a function to count the number of even and odd values in the list. He has written the following code but his code is having errors. Rewrite the correct code and underline the corrections made.
define EOCOUNT(L):
even_no=odd_no=0
for i in range(0,len(L))
    if L[i]%2=0:
        even_no+=1
    Else:
        odd_no+=1
print (even_no, odd_no)

Q3. [Short Answer] [2M] [Easy] Section-B
The code given below accepts a number as an argument and returns the reverse number. Observe the following code carefully and rewrite it after removing all syntax and logical errors. Underline all the corrections made.
define revNumber(num):
    rev = 0
    rem = 0
    While num > 0:
        rem ==num %10
        rev = rev*10 + rem
        num = num//10
        return rev
print(revNumber(1234))

Q4. [Programming] [3M] [Medium] Section-C
Write a function EOReplace() in Python, which accepts a list L of numbers. Thereafter, it increments all even numbers by 1 and decrements all odd numbers by 1.
Example :
If Sample Input data of the list is :
L=[10,20,30,40, 35,55]
Output will be :
L=[11,21,31,41,34,54]

Q5. [Programming] [3M] [Medium] Section-C
Write a function search_replace() in Python which accepts a list L of numbers and a number to be searched. If the number exists, it is replaced by 0 and if the number does not exist, an appropriate message is displayed.
Example :
L = [10,20,30,10,40]
Number to be searched = 10
List after replacement :
L = [0,20,30,0,40]

--- 2024 Board Exam (4 questions | 8 marks) ---

Q1. [Programming] [2M] [Easy] Section-B
Observe the following code carefully and rewrite it after removing all syntactical errors. Underline all the corrections made.
def 1func():
    a=input("Enter a number")
    if a>=33
        print("Promoted to next class")
    ELSE:
        print("Repeat")

Q2. [Programming] [2M] [Easy] Section-B
(a) Write the definition of a method/function SearchOut(Teachers, TName) to search for TName from a list Teachers, and display the position of its presence.
For example :
If the Teachers contain ["Ankit", "Siddharth", "Rahul", "Sangeeta", "rahul"] and TName contains "Rahul"
The function should display
Rahul at 2
rahul at 4

Q3. [Programming] [2M] [Easy] Section-B
(b) Write the definition of a method/function Copy_Prime(lst) to copy all the prime numbers from the list lst to another list lst_prime.

Q4. [Short Answer] [2M] [Easy] Section-B
The code provided below is intended to swap the first and last elements of a given tuple. However, there are syntax and logical errors in the code. Rewrite it after removing all errors. Underline all the corrections made.
def swap_first_last(tup)
    if len(tup) < 2:
        return tup
    new_tup = (tup[-1],) + tup[1:-1] + (tup[0])
    return new_tup
result = swap_first_last((1, 2, 3, 4))
print("Swapped tuple: " result)

--- 2025 Board Exam (4 questions | 7 marks) ---

Q1. [MCQ] [1M] [Easy] Section-A
Consider the statements given below and then choose the correct output from the given options:
def Change(N):
    N=N+10
    print(N,end='$$')
N=15
Change(N)
print(N)
(A) 25$$15
(B) 15$$25
(C) 25$$25
(D) 2525$8

Q2. [Programming] [2M] [Easy] Section-B
The code provided below is intended to remove the first and last characters of a given string and return the resulting string. However, there are syntax and logical errors in the code.
Rewrite it after removing all the errors. Also, underline all the corrections made.
define remove_first_last(str):
    if len(str) < 2:
        return str
    new_str = str[1:-2]
    return new_str
result = remove_first_last("Hello")
Print("Resulting string: " result)

Q3. [Programming] [2M] [Easy] Section-B
A. Write a function remove_element() in Python that accepts a list L and a number n. If the number n exists in the list, it should be removed. If it does not exist, print a message saying "Element not found".

Q4. [Programming] [2M] [Easy] Section-B
B. Write a Python function add_contact() that accepts a dictionary phone_book, a name, and a phone number. The function should add the name and phone number to the dictionary. If the name already exists, print "Contact already exists" instead of updating it.

--- 2026 Board Exam (1 question | 2 marks) ---

Q1. [Programming] [2M] [Easy] Section-B
The function given below is written to accept a string s as a parameter and return the number of vowels appearing in the string. The code has certain errors. Observe the code carefully and rewrite it after removing all the logical and syntax errors. Underline all the corrections made.
def CountVowels(s):
    c=0
    for ch in range(s):
        if 'aeiouAEIOU' in ch:
            c=+1
    return(ch)

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===========================================
QUESTION PATTERN BANK (What the board actually asks for THIS topic)
===========================================
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: Function definition call and return
  Pattern: MCQ=4, Programming=11, Short Answer=3 | Marks: 1M=4, 2M=12, 3M=2 | Total: 18 questions
  [MCQ] [1M] [Easy] × 2
    → Core concept of Function definition call and return
  [MCQ] [1M] [Easy] × 2
    → Output/result interpretation for the current concept
  [Short Answer] [2M] [Easy]
    → Core concept of Function definition call and return
  [Programming] [2M] [Easy] × 7
    → Core concept of Function definition call and return
  [Short Answer] [2M] [Easy] × 2
    → Exception can occur even when syntax is correct
  [Programming] [3M] [Medium]
    → Output/result interpretation for the current concept
  [Programming] [3M] [Medium]
    → Core concept of Function definition call and return
  [Programming] [2M] [Easy] × 2
    → Exception can occur even when syntax is correct


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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 | Function definition call and return | 100 | 18 | 34M | 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
===========================================

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 "Function definition, call and return". Self-generate 4–7 traps from:
- actual question patterns for Function definition call and return
- 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">
<title>Function definition, call and return PYQ — Lecture 15</title>
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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">Function definition, call and return PYQ — Lecture 15</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 with full + compressed coverage]

<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: Function definition call and return).
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)
* No HOTS question (the provided PYQs do not reveal a 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 + Compressed Coverage (18 source questions)</h2>
[This source pool has 18 actual PYQs.
PYQ COVERAGE RULE:
  - If the PYQ pool has 15 or fewer questions, include and discuss ALL actual PYQs in Section 7.
  - Do not compress, replace, paraphrase, or skip any actual PYQ in a small pool.
  - This pool has more than 15 questions: fully discuss the highest-yield 15 and compactly
    list the rest with concept tested + exam trap.
  - 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;

For compressed representative questions, label them "Representative PYQ-pattern question", not as a real board question, and never show a fake year, marks, or section.]

<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 "Function definition, call and return" — zero content from other topics
- PYQ lecture: fully discuss the highest-yield 15 and compactly list the rest with concept tested + exam trap; compression is allowed only because this pool exceeds 15
- 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 + Compressed 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 "Function definition, call and return") 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).