O Level / IGCSE Computer Science chapter 2: Data transmission MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
28 exam-style questions on Data transmission, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A company encrypts customer data it sends over the internet. A hacker intercepts the transmission. Which statement is correct?
A
the hacker cannot capture the data at all
B
the data is deleted automatically when intercepted
C
the hacker can read the data but cannot change it, because it is encrypted
D
the hacker has the data but cannot understand it without the key
Show answer
Answer: D. Interception is still possible. Encryption means the captured data is ciphertext, which is useless without the decryption key.
2. Which is a benefit of the universal serial bus (USB) interface?
A
a connected device is detected automatically and the correct driver is loaded
B
USB cables can be several kilometres long
C
USB sends data in parallel along many wires, so it is always the fastest interface available
D
USB devices do not need a driver of any kind
Show answer
Answer: A. USB is a standard: devices are recognised automatically when plugged in and their drivers are loaded; the connector can also supply power. Cable length is limited to a few metres.
3. A block of bytes is sent with a parity byte, so every row and every column has a parity bit. On arrival, only row 3 and only column 5 have incorrect parity. What does this show?
A
the bit in row 3, column 5 was changed and can be corrected
B
all of row 3 and all of column 5 must be sent again
C
the parity byte itself is wrong, so the data bytes are all correct
D
two different bits have been changed
Show answer
Answer: A. A single flipped bit makes both its row and its column fail the check. The intersection pinpoints the bit, so it can be flipped back.
4. Which set of items is held in the header of a data packet?
the addresses of every router the packet will pass through on its route
D
file name, packet number, parity block
Show answer
Answer: A. The header holds the destination address, the packet number and the originator’s (sender’s) address. The payload is the actual data, and the trailer is a separate part of the packet.
5. How does a checksum detect an error in transmitted data?
A
the receiver sends all of the data back to the sender, which compares it with the original copy it kept
B
the receiver sends a timeout message if no data arrives
C
an extra bit is added to each byte so the number of 1s is even
D
the sender calculates a value from the data and sends it; the receiver recalculates and compares
Show answer
Answer: D. The sender calculates a checksum from the block using an agreed method and sends it with the data. The receiver repeats the calculation; if the values differ, an error occurred. Sending data back is an echo check.
6. Ali wants to send Bina a confidential message using asymmetric encryption. Which key does Ali use to encrypt it?
A
Ali’s private key
B
Ali’s public key
C
Bina’s private key
D
Bina’s public key
Show answer
Answer: D. The message is encrypted with the receiver’s public key, which anyone may have. Only the matching private key, held by Bina, can decrypt it.
7. What is symmetric encryption?
A
the same key is used to encrypt and to decrypt the data
B
a public key encrypts and a private key decrypts
C
the data is encrypted twice using two different keys
D
the data is encrypted in both directions at the same time
Show answer
Answer: A. Symmetric encryption uses one shared secret key for both processes. Using a public and a private key is asymmetric encryption.
8. What is the main security problem with symmetric encryption?
A
it cannot encrypt images
B
anyone who has a copy of the public key is then able to decrypt the data
C
the ciphertext is always larger than the original
D
the key has to be shared with the receiver, and could be intercepted
Show answer
Answer: D. Both sides need the same key, so it must be sent to the receiver somehow. If the key is intercepted, all messages using it can be decrypted.
9. In an echo check the data returned to the sender does not match the original. What is a weakness of this method?
A
it cannot show whether the error happened on the way there or on the way back
B
echo checks can only check one byte at a time, so long files cannot be checked
C
echo checks cannot detect any errors in the data
D
the receiver must know the checksum formula before any data can be checked
Show answer
Answer: A. The data travels twice, so a mismatch may be caused by an error in either journey. The data must be sent again even if the receiver’s copy was correct.
10. When is a check digit used?
A
after packets have been transmitted, to find any bits changed by interference on the way
B
to encrypt a barcode so it cannot be copied
C
to decide the route a packet takes
D
when a code such as an ISBN or barcode is entered, to detect data entry errors
Show answer
Answer: D. A check digit is calculated from the other digits and stored as the last digit. When the number is typed or scanned, it is recalculated to spot entry errors such as a wrong or swapped digit.
28, each with the answer and a short explanation, across 3 topics: Types and methods of data transmission, Methods of error detection, Encryption. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Computer Science chapter 2 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
