It contains multiple choice questions for students better understanding

1. Blockchain Technology MCQ
-MENAKA DEVI.M

2. 1) Which problem primarily motivated the shift from digital money to distributed ledgers?
Options:
A. Double-spending without a trusted authority
B. High transaction fees
C. Slow internet speeds
D. Poor user interfaces

3. Correct Answer: A
Explanation: Digital money could be copied and reused without a shared verification system.

4. 2) Early digital money systems failed mainly because they were:
Options:
A. Permissionless
B. Transparent
C. Decentralized
D. Centrally controlled

5. Correct Answer: D
Explanation: Central control created trust and failure issues.

6. 3) A distributed ledger differs from a traditional database because it is:
Options:
A. Faster
B. Replicated across multiple nodes
C. Stored locally
D. Password protected

7. Correct Answer: B
Explanation: The ledger is shared and synchronized across many nodes.

8. 4) Which design primitive defines the communication rules in blockchain?
Options:
A. Consensus
B. Mining
C. Protocols
D. Hashing

9. Correct Answer: C
Explanation: Protocols specify how nodes interact and exchange data.

10. 5) Blockchain security mainly depends on:
Options:
A. Firewalls
B. Cryptographic primitives
C. User passwords
D. Physical security

11. Correct Answer: B
Explanation: Hash functions and digital signatures secure the system.

12. 6) Consensus in blockchain determines:
Options:
A. Network speed
B. Transaction fees
C. Block size
D. The valid next block

13. Correct Answer: D
Explanation: Consensus ensures agreement on which block to add next.

14. 7) Permissions in a blockchain system decide:
Options:
A. Who can read or write data
B. Hash algorithm type
C. Block creation time
D. Network topology

15. Correct Answer: A
Explanation: Permissions control access rights in the network.

16. 8) Which blockchain allows anyone to participate without approval?
Options:
A. Private
B. Consortium
C. Permissioned
D. Permissionless

17. Correct Answer: D
Explanation: Permissionless blockchains are open to all users.

18. 9) Privacy is difficult in blockchain mainly because:
Options:
A. Blocks are encrypted
B. Nodes are centralized
C. Data is transparent and distributed
D. Consensus is slow

19. Correct Answer: C
Explanation: All nodes can view the shared ledger.

20. 10) What cryptographically links one block to the previous block?
Options: A. Timestamp
B. Merkle root
C. Hash pointer
D. Digital signature

21. Correct Answer: C
Explanation: Each block stores the hash of the previous block.

22. 11) Blockchain networks primarily follow which architecture?
Options:
A. Client-server
B. Peer-to-peer
C. Hierarchical
D. Centralized

23. Correct Answer: B
Explanation: Nodes communicate directly without a central authority.

24. 12) What is the effect of modifying a block’s data?
Options:
A. Only the block changes
B. The chain auto-corrects
C. Hash remains same
D. The entire chain becomes invalid

25. Correct Answer: D
Explanation: Changed data breaks hash links across the chain.

26. 13)what is the primary purpose of storing the <Previous Hash= in each block?
Options:
A. To reduce the size of the blockchain
B. To enable faster mining of blocks
C. To maintain immutability and detect tampering
D. To encrypt transaction data

27. Correct Answer:C
Explanation:Because each block stores the hash of the previous block, any change in a block alters its
hash and breaks the chain, making tampering immediately detectable.

28. 14) Which hashing property prevents two inputs from producing the same hash?
Options:
A. Compression
B. Speed
C. Determinism
D. Collision resistance

29. Correct Answer: D
Explanation: Collision resistance ensures unique hash outputs.

30. 15) Digital signatures mainly provide:
Options:
A. Authentication and non-repudiation
B. Encryption
C. Data compression
D. Faster transactions

31. Correct Answer: A
Explanation: They verify identity and prevent denial.

32. 16) Which key is used to create a digital signature?
Options:
A. Public key
B. Network key
C. Private key
D. Shared key

33. Correct Answer: C
Explanation: Only the private key holder can sign data.

34. 17) A hash chain is formed by:
Options:
A. Encrypting blocks
B. Linking hashes sequentially
C. Broadcasting hashes
D. Signing blocks

35. Correct Answer: B
Explanation: Each hash depends on the previous hash.

36. 18) Why are hash chains important in blockchain?
Options:
A. Increase speed
B. Reduce storage
C. Enable encryption
D. Ensure tamper resistance

37. Correct Answer: D
Explanation: Any data change breaks the chain.

38. 19) Blockchain improves basic hash chains by adding:
Options:
A. Timestamping and consensus
B. Password protection
C. Central authority
D. Firewalls

39. Correct Answer: A
Explanation: These ensure ordering and agreement

40. 20) Which feature prevents a single node from rewriting history?
Options:
A. Wallet software
B. Consensus mechanism
C. Network layer
D. User interface

41. Correct Answer: B
Explanation: Ledger changes require majority approval.

42. 21) Why is consensus essential in a distributed ledger?
Options:
A. To increase block size
B. To reduce encryption cost
C. To synchronize user wallets
D. To ensure agreement among untrusted nodes

43. Correct Answer: D
Explanation: Nodes do not trust each other, so consensus ensures agreement.

44. 22)Proof of Work secures blockchain mainly by using:
Options:
A. Identity verification
B. Economic penalties
C. Computational difficulty
D. Voting power

45. Correct Answer: C
Explanation: Miners must solve complex puzzles to add blocks.

46. 23)Which factor makes Proof of Work resistant to attacks?
Options:
A. High energy and computation cost
B. Centralized control
C. Permissioned access
D. Fast block generation

47. Correct Answer: A
Explanation: Attacks require enormous computational power.

48. 24)Proof of Stake selects validators based on:
Options:
A. Network speed
B. Amount of cryptocurrency locked
C. Hashing power
D. Time spent online

49. Correct Answer: B
Explanation: Validators are chosen according to their stake.

50. 25)Which consensus mechanism reduces energy consumption the most?
Options:
A. Proof of Work
B. Proof of Authority
C. Proof of Stake
D. Proof of Delay

51. Correct Answer: C
Explanation: It avoids heavy computational mining.

52. 26)Byzantine Fault Tolerance focuses on handling:
Options:
A. Network congestion
B. Malicious or faulty nodes
C. Hash collisions
D. Key loss

53. Correct Answer: B
Explanation: It works even if some nodes behave incorrectly.

54. 27)A permissioned blockchain mainly differs from a public
blockchain in:
Options:
A. Use of cryptography
B. Block structure
C. Transaction format
D. Access control

55. Correct Answer: D
Explanation: Participation is restricted to authorized entities

56. 28)Which layer of blockchain handles peer discovery and
message propagation?
Options:
A. Application layer
B. Consensus layer
C. Network layer
D. Data layer

57. Correct Answer: C
Explanation: The network layer connects and communicates between nodes.

58. 29)Merkle trees are used in blockchain to:
Options:
A. Encrypt transactions
B. Reduce transaction verification time
C. Generate private keys
D. Select validators

59. Correct Answer: B
Explanation: They allow efficient and fast verification of transactions.

60. 30)Which technique allows proving transaction validity without
revealing data?
Options:
A. Digital signatures
B. Hashing
C. Symmetric encryption
D. Zero-knowledge proofs

61. Correct Answer: D
Explanation: Validity is proven without exposing information.

62. 31)Decentralization in blockchain primarily ensures:
Options:
A. Faster transactions
B. Lower storage
C. No single point of control
D. Hidden identities

63. Correct Answer: C
Explanation: Control is distributed among many nodes.

64. 32)Bitcoin’s major contribution was combining cryptography
with:
Options:
A. Central banking
B. Distributed consensus
C. Cloud storage
D. Artificial intelligence

65. Correct Answer: B
Explanation: It enabled trustless peer-to-peer transactions.

66. 33)Blockchain immutability means:
Options:
A. Data cannot be deleted easily
B. Data is encrypted
C. Data is centrally stored
D. Data can never be viewed

67. Correct Answer: A
Explanation: Once recorded, data cannot be altered easily.

68. 34)Which cryptographic primitive verifies the sender of a transaction?
Options:
A. Hash function
B. Timestamp
C. Digital signature
D. Merkle root

69. Correct Answer: C
Explanation: Digital signatures authenticate the sender.

70. 35)Which cryptographic primitive verifies the sender of a transaction?
Options:
A. Hash function
B. Timestamp
C. Digital signature
D. Merkle root

71. Correct Answer: C
Explanation: Digital signatures authenticate the sender.

72. 36)Blockchain protocols mainly define:
Options:
A. Token prices
B. Network rules and behavior
C. Wallet addresses
D. Hash output size

73. Correct Answer: B
Explanation: Protocols govern how the system operates.

74. 37)When two blocks are mined at the same time, the result is:
Options:
A. Network failure
B. Permanent split
C. Data loss
D. Temporary fork

75. Correct Answer: D
Explanation: The network briefly diverges until consensus resolves it.

76. 38)The longest chain rule helps the blockchain to:
Options:
A. Increase speed
B. Reduce storage
C. Resolve forks
D. Encrypt data

77. Correct Answer: C
Explanation: The longest valid chain is accepted as correct.

78. 39)Which property ensures that a small input change drastically changes the hash?
Options:
A. Determinism
B. Collision resistance
C. Avalanche effect
D. Compression

79. Correct Answer: C
Explanation: Minor changes produce completely different hashes.

80. 40)Public blockchains prioritize which design principle the most?
Options:
A. Confidentiality
B. Transparency
C. Central authority
D. Restricted access

81. Correct Answer: B
Explanation: All transactions are openly visible.

82. 41)The blockchain ledger primarily stores
Options:
A. User passwords
B. Private keys
C. Transaction history
D. Consensus algorithms

83. Correct Answer: C
Explanation: All confirmed transactions are recorded in the ledger.

84. 42)Why is consensus harder in distributed systems?
Options:
A. Nodes are identical
B. Networks are fast
C. Data is encrypted
D. Nodes may behave maliciously

85. Correct Answer: D
Explanation: Some nodes may act dishonestly or fail.

86. 43)Nodes validate transactions by:
Options:
A. Trusting miners
B. Recomputing cryptographic hashes
C. Asking a central server
D. Using passwords

87. Correct Answer: B
Explanation: Independent verification ensures correctness.

88. 44)Private blockchains are best suited for:
Options:
A. Open cryptocurrencies
B. Anonymous trading
C. Enterprise or organizational use
D. Public voting

89. Correct Answer: C
Explanation: They require controlled participation.

90. 45)Which element ensures the chronological order of blocks?
Options:
A. Timestamp
B. Merkle tree
C. Signature
D. Public key

91. Correct Answer: A
Explanation: Timestamps record when blocks are created.

92. 46)Digital signatures do NOT provide:
Options:
A. Authentication
B. Integrity
C. Confidentiality
D. Non-repudiation

93. Correct Answer: C
Explanation: Signatures do not encrypt data.

94. 47)Hash collisions are dangerous because they break:
Options:
A. Speed
B. Data integrity
C. Network topology
D. Key ownership

95. Correct Answer: B
Explanation: Different data producing same hash damages trust.

96. 48)Which layer is responsible for maintaining copies of the ledger?
Options:
A. Application layer
B. Network layer
C. Data layer
D. Consensus layer

97. Correct Answer: C
Explanation: The data layer stores blockchain records.

98. 49)Blockchain addresses are considered pseudonymous because:
Options:
A. They hide all transactions
B. They are encrypted identities
C. They change daily
D. They are not directly linked to real identities

99. Correct Answer: D
Explanation: Addresses do not automatically reveal user identity.

100. 50)Blockchain security depends most on:
Options:
A. User interface design
B. Token value
C. Cryptographic strength
D. Network speed

101. Correct Answer: C
Explanation: Weak cryptography compromises the system.

102. 51)Blockchain technology is best defined as:
Options:
A. A centralized database
B. A cloud storage service
C. A peer-to-peer payment app
D. A distributed, immutable ledger

103. Correct Answer: D
Explanation: Data is shared across nodes and cannot be easily altered.

104. THANK YOU
For your attention and participation.