Computer Science · Sample Paper 3

General instructions

Section A · Objective

1. Question 11 mark

   Software used to create and manage databases is a

   1. A.DBMS
   2. B.compiler
   3. C.browser
   4. D.spreadsheet
2. Question 21 mark

   A key that can uniquely identify rows but is not chosen as the primary key is an

   1. A.alternate key
   2. B.foreign key
   3. C.composite key
   4. D.super key only
3. Question 31 mark

   Which of these has the worst-case time complexity O(n²)?

   1. A.binary search
   2. B.linear search
   3. C.bubble sort
   4. D.accessing a list element
4. Question 41 mark

   Which exception is raised when dividing by zero?

   1. A.ValueError
   2. B.ZeroDivisionError
   3. C.TypeError
   4. D.IndexError
5. Question 51 mark

   The else block in try–except runs when

   1. A.an exception occurs
   2. B.no exception occurs
   3. C.always
   4. D.never
6. Question 61 mark

   Which mode opens a file for reading and writing without truncating it?

   1. A.'w+'
   2. B.'r+'
   3. C.'a'
   4. D.'x'
7. Question 71 mark

   Which function writes a Python object to a binary file?

   1. A.pickle.load()
   2. B.pickle.dump()
   3. C.write()
   4. D.csv.writer()
8. Question 81 mark

   Removing the top element of a stack is called

   1. A.push
   2. B.pop
   3. C.peek
   4. D.enqueue
9. Question 91 mark

   The infix form of the postfix expression 'A B C * +' is

   1. A.(A + B) * C
   2. B.A + B * C
   3. C.A * B + C
   4. D.A + (B + C)
10. Question 101 mark

    Inserting an element into a queue is called

    1. A.push
    2. B.enqueue
    3. C.dequeue
    4. D.pop
11. Question 111 mark

    After the first pass of bubble sort (ascending) on [5, 1, 4, 2], the list is

    1. A.[1, 4, 2, 5]
    2. B.[1, 5, 4, 2]
    3. C.[1, 2, 4, 5]
    4. D.[5, 4, 2, 1]
12. Question 121 mark

    The maximum number of comparisons in binary search on 16 sorted elements is about

    1. A.4–5
    2. B.8
    3. C.16
    4. D.2
13. Question 131 mark

    Data that can be stored in rows and columns is called

    1. A.unstructured data
    2. B.structured data
    3. C.metadata
    4. D.big data only
14. Question 141 mark

    Which constraint ensures a column cannot have NULL values?

    1. A.UNIQUE
    2. B.NOT NULL
    3. C.DEFAULT
    4. D.CHECK
15. Question 151 mark

    SELECT DISTINCT city FROM customer; returns

    1. A.all cities with repeats
    2. B.each city only once
    3. C.the number of cities
    4. D.an error
16. Question 161 mark

    Which device connects a computer to the internet over telephone lines by modulating signals?

    1. A.router
    2. B.modem
    3. C.hub
    4. D.switch
17. Question 171 mark

    A network of computers within a building is a

    1. A.WAN
    2. B.MAN
    3. C.LAN
    4. D.PAN
18. Question 181 mark

    Which protocol is used to transfer web pages?

    1. A.SMTP
    2. B.HTTP
    3. C.FTP
    4. D.POP3
19. Question 191 mark

    Unauthorised access to a computer system is

    1. A.hacking
    2. B.browsing
    3. C.backup
    4. D.encryption
20. Question 201 mark

    Assertion (A): Insertion sort is efficient for nearly sorted lists.

    Reason (R): In a nearly sorted list, few elements need to be shifted.

    1. A.Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
    2. B.Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
    3. C.Assertion (A) is true, but Reason (R) is false.
    4. D.Assertion (A) is false, but Reason (R) is true.
21. Question 211 mark

    Assertion (A): A switch is more efficient than a hub.

    Reason (R): A switch sends data only to the intended device, while a hub broadcasts to all.

    1. A.Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
    2. B.Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
    3. C.Assertion (A) is true, but Reason (R) is false.
    4. D.Assertion (A) is false, but Reason (R) is true.

Section B · Very short answer

1. Question 222 marks

   What is meant by the degree and cardinality of a relation? Give an example.

2. Question 232 marks

   Write the output:

   try:
       x = int('12a')
   except ValueError:
       print('Invalid')
   finally:
       print('End')
   

3. OR

   Question 232 marks

   What is the purpose of the finally block? Give one situation where it is useful.

4. Question 242 marks

   Write a function display_long() that displays the lines of poem.txt that have more than 30 characters.

5. Question 252 marks

   Convert the infix expression (A + B) * (C − D) to postfix, showing the stack steps briefly.

6. Question 262 marks

   Differentiate between CHAR and VARCHAR data types in SQL.

7. Question 272 marks

   Expand: (i) TCP/IP (ii) VoIP (iii) HTML (iv) LAN.

8. Question 282 marks

   What is two-factor authentication? Give an example.

Section C · Short answer

1. Question 293 marks

   Write functions enqueue(q, item) and dequeue(q) for a queue implemented as a list; dequeue should print 'Underflow' if the queue is empty.

2. OR

   Question 293 marks

   Show the steps of binary search for 23 in [4, 8, 15, 16, 23, 42, 50].

3. Question 303 marks

   Write a program to read students.csv (columns: roll, name, marks) and print the names of students who scored above 90.

4. Question 313 marks

   Distinguish between guided and unguided transmission media with two examples of each.

Section D · Long answer

1. Question 324 marks

   Consider the table STUDENT:

   | RollNo | Name | Class | Marks | City | |---|---|---|---|---| | 1 | Asha | 12 | 88 | Delhi | | 2 | Ravi | 11 | 72 | Pune | | 3 | Meena | 12 | 95 | Delhi | | 4 | Arjun | 12 | 65 | Mumbai |

   Write SQL queries to:

   (i) display the names of students from Delhi, (ii) display the average marks of class 12 students, (iii) display the details of students whose name starts with 'A', (iv) display the number of students in each city.

2. Question 334 marks

   Write a program that copies only those lines from source.txt to target.txt which do not start with the character '#'.

3. Question 344 marks

   Write a Python program using mysql.connector to display all records from the table EMP of database office where salary is greater than 50000.

4. OR

   Question 344 marks

   Differentiate between DELETE and DROP commands, and between ALTER and UPDATE commands, with examples.

5. Question 354 marks

   Explain the star, bus, ring and tree topologies with one advantage of each.

Section E · Long answer

1. Question 365 marks

   Case study — School campus network. A school in Jaipur has four blocks: ADMIN, SCIENCE, JUNIOR and SPORTS. Distances: ADMIN–SCIENCE 80 m, ADMIN–JUNIOR 150 m, ADMIN–SPORTS 120 m, SCIENCE–JUNIOR 60 m, SCIENCE–SPORTS 90 m, JUNIOR–SPORTS 70 m. Computers: ADMIN 30, SCIENCE 80, JUNIOR 40, SPORTS 10.

   (i) Suggest the best block for the server, with a reason. (1 mark)

   (ii) Suggest a cable layout to connect the blocks. (1 mark)

   (iii) Which device should be used to connect computers within each block? (1 mark)

   (iv) The school wants to connect to its branch in another city. What type of network is this? (1 mark)

   (v) Suggest a cost-effective way to provide internet in the SPORTS block, which is far from others. (1 mark)

2. Question 375 marks

   Write a program that uses a stack to reverse a string entered by the user, and then checks whether the string is a palindrome.

3. OR

   Question 375 marks

   Write a menu-driven program to (1) add a record [itemno, name, price] to the binary file items.dat, (2) display all records, (3) search for an item by item number.