CBSE Class 11 Computer Science — NCERT Solutions

Given: We need to identify the software that makes a computer functional and state its two primary services.

Answer:

The software required to make a computer functional is the Operating System (OS).

Examples: Windows, Linux, macOS, Ubuntu.

Two Primary Services of an Operating System:

1. Process Management: The operating system manages the execution of processes (programs in execution). It schedules processes, allocates CPU time, and ensures that multiple processes can run efficiently without conflict.

2. Memory Management: The operating system manages the primary (main) memory of the computer. It keeps track of each memory location — whether it is free or occupied — and allocates/deallocates memory to processes as needed, ensuring maximum utilisation of available memory.

Given: A program is written in a high-level language (e.g., Python, C++, Java).

Concept: A computer can only understand machine code (binary language — 0s and 1s). It cannot directly understand high-level language instructions.

Answer:

A program written in a high-level language (called source code) must be translated into machine code (binary code) before the computer can execute it. This translation is done by special system software called translators, which are of the following types:

1. Compiler: Translates the entire source code into machine code at once, producing an executable file. The compiled machine code can then be executed directly by the CPU.

2. Interpreter: Translates and executes the source code line by line, one statement at a time.

3. Assembler: Converts assembly language code into machine code.

Thus, the computer understands a high-level language program only after it has been converted into machine code by a compiler or interpreter.

The base (radix) of a number system equals the total number of unique digits (symbols) it uses.

• Binary base = 2
• Octal base = 8
• Hexadecimal base = 16

ASCII — American Standard Code for Information Interchange

ISCII — Indian Script Code for Information Interchange

ASCII is a 7-bit (or 8-bit extended) encoding scheme used to represent English characters and control characters. ISCII is an 8-bit encoding scheme developed to represent characters of Indian scripts.

Cloud-based services commonly used today include:

1. Google Drive / OneDrive / Dropbox – Cloud storage for files, photos and documents.
2. Gmail / Outlook – Web-based email services hosted on the cloud.
3. Google Docs / Microsoft 365 – Online word processing, spreadsheets and presentations.
4. YouTube / Netflix / Hotstar – Cloud-based video streaming platforms.
5. Google Classroom / DIKSHA – Cloud-based e-learning platforms.
6. WhatsApp / Telegram – Messaging apps that store media and chats on the cloud.
7. iCloud / Google Photos – Automatic cloud backup of photos and contacts.
8. Zoom / Google Meet – Cloud-based video conferencing services.

All these services allow users to access data and applications from any device connected to the internet, without needing local storage or processing power.

Internet of Things (IoT):

The Internet of Things (IoT) is a network of physical devices (things) embedded with sensors, software, and other technologies that enable them to connect and exchange data with other devices and systems over the internet — without requiring human-to-human or human-to-computer interaction.

Key idea: Everyday objects become 'smart' by being connected to the internet.

Potential Applications of IoT:

Thus, IoT connects the physical world to the digital world, enabling automation and real-time monitoring across virtually every sector.

Given: Two numbers are to be read; one is divided by the other and the quotient is displayed.

Concept: Sequential algorithm with input, process, and output steps.

Pseudocode:

BEGIN
  READ num1, num2
  IF num2 ≠ 0 THEN
    quotient ← num1 / num2
    PRINT quotient
  ELSE
    PRINT "Division by zero is not allowed"
  END IF
END

Explanation:

• num1 and num2 are the two numbers entered by the user.
• Before dividing, we check that the divisor (num2) is not zero to avoid an undefined operation.
• The result is stored in quotient and then printed.

Rules for valid Python identifiers:

• Must begin with a letter (A–Z or a–z) or an underscore (_).
• Can contain letters, digits (0–9), and underscores only.
• Cannot be a Python keyword.
• No spaces or special characters allowed.

i. Serial_no. — Invalid. Contains a dot (.), which is not allowed in an identifier.

ii. 1st_Room — Invalid. Starts with a digit (1), which is not permitted.

**iii. Hundred$** — **Invalid**. Contains a special character ($), which is not allowed.

iv. Total Marks — Invalid. Contains a space, which is not allowed.

v. Total_Marks — Valid. Starts with a letter and contains only letters and an underscore.

vi. total-Marks — Invalid. Contains a hyphen (-), which is not allowed (it is interpreted as the minus operator).

vii. Percentage — Valid. Starts with a letter and contains only letters.

viii. True — Invalid. True is a reserved keyword in Python and cannot be used as an identifier.

Given: Two constructs of the if statement — else and elif.

Concept: Both are used with the if statement for decision making, but they serve different purposes.

Example:

# Using else
x = 5
if x > 10:
    print("Greater than 10")
else:
    print("Not greater than 10")   # This executes

# Using elif
marks = 75
if marks >= 90:
    print("Grade A")
elif marks >= 75:
    print("Grade B")   # This executes
elif marks >= 60:
    print("Grade C")
else:
    print("Grade D")

Conclusion: else provides one alternative when the if condition is False, whereas elif allows checking multiple conditions in sequence.

Errors identified:

1. print text — In Python 3, print is a function and must be called with parentheses. It should be print(text).

2. create(5) — The function create is defined with two parameters (text and freq), but the function call passes only one argument. It should be something like create("Hello", 5).

3. range(1, freq) — This will print text only freq - 1 times (from 1 to freq-1). If the intent is to print freq times, it should be range(1, freq+1) or range(freq).

Corrected Code:

def create(text, freq):
    for i in range(1, freq + 1):
        print(text)
create("Hello", 5)  # function call

Given: mySubject = "Computer Science"

The string has 16 characters (indices 0 to 15).

$$\text{C o m p u t e r S c i e n c e}$$
$$\text{0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15}$$

i. print(mySubject[0:len(mySubject)])

len(mySubject) = 16, so mySubject[0:16] returns the entire string.

Output:

Computer Science

ii. print(mySubject[-7:-1])

Negative index $-7$ corresponds to index $16 - 7 = 9$ (character S) and $-1$ corresponds to index $15$ (exclusive), so characters at indices 9 to 14 are returned: S, c, i, e, n, c.

Output:

Scienc

iii. print(mySubject[::2])

Slice with step 2 picks every alternate character starting from index 0:

• Indices: 0(C), 2(m), 4(u), 6(e), 8( ), 10(c), 12(e), 14(c)

Output:

Cmue ce

iv. print(mySubject[len(mySubject)-1])

len(mySubject) - 1 = 15, so mySubject[15] = 'e' (last character).

Output:

e

**v. print(2*mySubject)**

The * operator repeats the string 2 times.

Output:

Computer ScienceComputer Science

vi. print(mySubject[::-2])

Slice with step $-2$ starts from the last character (index 15) and moves backwards picking every alternate character:

• Indices: 15(e), 13(n), 11(i), 9(S), 7(r), 5(t), 3(p), 1(o)

Output:

eniSrtpo

vii. print(mySubject[:3] + mySubject[3:])

mySubject[:3] = "Com" and mySubject[3:] = "puter Science". Concatenating them gives back the full string.

Output:

Computer Science

viii. print(mySubject.swapcase())

swapcase() converts uppercase letters to lowercase and vice versa.

• C → c, o → O, m → M, p → P, u → U, t → T, e → E, r → R, space stays, S → s, c → C, i → I, e → E, n → N, c → C, e → E

Output:

cOMPUTER sCIENCE

ix. print(mySubject.startswith('Comp'))

startswith() returns True if the string starts with the given prefix. "Computer Science" does start with "Comp".

(Note: The question has a typo startsworth; the correct method is startswith.)

Output:

True

x. print(mySubject.isalpha())

isalpha() returns True only if all characters are alphabetic. "Computer Science" contains a space, so it returns False.

Output:

False

Given: A list list1 = [12,32,65,26,80,10]

Concept: list1.sort() sorts the list in-place in ascending order and modifies the original list.

Working:

• Original list: [12, 32, 65, 26, 80, 10]
• After list1.sort(): elements are arranged in ascending order → [10, 12, 26, 32, 65, 80]
• print(list1) prints the modified list.

Output:

[10, 12, 26, 32, 65, 80]

Given:
$$\text{tuple1} = (23, 1, 45, 67, 45, 9, 55, 45)$$
$$\text{tuple2} = (100, 200)$$

i. print(tuple1.index(45))

The index() method returns the index of the first occurrence of the given element.

In tuple1, 45 first appears at index 2 (0-based indexing).

$$\boxed{\text{Output: } 2}$$

ii. print(tuple1.count(45))

The count() method returns the number of times the element appears in the tuple.

45 appears at indices 2, 4, and 7 — a total of 3 times.

$$\boxed{\text{Output: } 3}$$

iii. print(tuple1 + tuple2)

The + operator concatenates two tuples.

$$\text{tuple1} + \text{tuple2} = (23, 1, 45, 67, 45, 9, 55, 45, 100, 200)$$

$$\boxed{\text{Output: } (23, 1, 45, 67, 45, 9, 55, 45, 100, 200)}$$

iv. print(len(tuple2))

The len() function returns the number of elements in the tuple.

tuple2 has 2 elements: 100 and 200.

$$\boxed{\text{Output: } 2}$$

v. print(max(tuple1))

The max() function returns the largest element.

Elements of tuple1: 23, 1, 45, 67, 45, 9, 55, 45. The maximum is 67.

$$\boxed{\text{Output: } 67}$$

vi. print(min(tuple1))

The min() function returns the smallest element.

Elements of tuple1: 23, 1, 45, 67, 45, 9, 55, 45. The minimum is 1.

$$\boxed{\text{Output: } 1}$$

vii. print(sum(tuple2))

The sum() function returns the sum of all elements.

$$100 + 200 = 300$$

$$\boxed{\text{Output: } 300}$$

viii. print(sorted(tuple1)) then print(tuple1)

The sorted() function returns a new sorted list from the tuple elements; the original tuple remains unchanged.

Sorted elements of tuple1 in ascending order: 1, 9, 23, 45, 45, 45, 55, 67.

Output of print(sorted(tuple1)):  [1, 9, 23, 45, 45, 45, 55, 67]
Output of print(tuple1):          (23, 1, 45, 67, 45, 9, 55, 45)

$$\boxed{\text{sorted(tuple1) gives a list } [1, 9, 23, 45, 45, 45, 55, 67]; \text{ tuple1 remains } (23, 1, 45, 67, 45, 9, 55, 45)}$$

Correct Answer: (b) Identity theft

Justification:

• Identity theft means using someone else's personal information (such as login credentials, email account, etc.) without their permission to impersonate them or carry out activities in their name.
• Revaan did not hack into Atharv's account by breaking any password or security system. He simply found the account already logged in and used it to send emails as if he were Atharv.
• By sending emails from Atharv's account, Revaan is pretending to be Atharv — this is a classic case of identity theft.
• It is not hacking (no security was broken), not plagiarism (no copying of content), and although the emails are inflammatory, the primary crime here is impersonating Atharv, i.e., identity theft.

Conclusion: Revaan's activity is an example of Identity Theft because he used Atharv's identity (email account) without authorisation to send messages, thereby misrepresenting himself as Atharv.