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Question 1. Which property ensures that blockchain data cannot be altered retroactively without consensus? A) Transparency B) Immutability C) Scalability D) Privacy Answer: B Explanation: Immutability guarantees that once data is recorded on the blockchain, it cannot be changed without network consensus. Question 2. What is the primary distinction between a public and a private blockchain? A) Public blockchains use proof-of-stake, private use proof-of-work B) Public blockchains are permissionless, private blockchains require permission C) Public blockchains have higher speed D) Private blockchains store data off-chain Answer: B Explanation: Public blockchains allow anyone to participate, while private blockchains restrict participation to approved entities. Question 3. Which consensus mechanism is most commonly used by Bitcoin? A) Proof of Stake B) Proof of Authority C) Practical Byzantine Fault Tolerance D) Proof of Work Answer: D Explanation: Bitcoin relies on Proof of Work, where miners solve cryptographic puzzles to validate transactions.
Question 4. In the Ethereum network, what is “gas” used for? A) Storing blockchain data B) Paying transaction fees C) Encrypting transactions D) Managing block rewards Answer: B Explanation: Gas is the fee required to execute operations on the Ethereum network. Question 5. Which cryptographic hash function is utilized by Bitcoin? A) MD B) SHA- 256 C) SHA- 1 D) Blake Answer: B Explanation: Bitcoin uses the SHA-256 hash algorithm for block hashing and mining. Question 6. What is a Merkle Tree used for in blockchain? A) Key generation B) Efficient verification of large data sets C) Network propagation D) Token standard implementation Answer: B Explanation: Merkle Trees enable efficient and secure verification of data in blocks.
Question 10. What is the role of digital signatures in blockchain transactions? A) Encrypting transaction data B) Validating ownership and authenticity C) Mining new blocks D) Defining token standards Answer: B Explanation: Digital signatures prove transaction authenticity and ownership. Question 11. What is the main function of a wallet in blockchain technology? A) Generate smart contracts B) Store private and public keys C) Mine blocks D) Verify transactions Answer: B Explanation: Wallets store keys needed to sign transactions and access funds. Question 12. What is a smart contract? A) A physical contract stored on the blockchain B) Self-executing code that enforces agreements C) A digital signature D) A type of node Answer: B Explanation: Smart contracts are programs that automatically execute predefined rules. Question 13. Which Solidity data type should be used to store a blockchain address?
A) uint B) bool C) address D) bytes Answer: C Explanation: The address type is specifically designed to store blockchain addresses. Question 14. What does the “require()” function do in Solidity? A) Reverts the transaction if a condition is false B) Generates random numbers C) Executes an external contract D) Logs events Answer: A Explanation: require() checks conditions and reverts the transaction if not met. Question 15. Which development framework allows for compiling, deploying, and testing Ethereum contracts? A) Ganache B) Truffle C) Remix IDE D) MetaMask Answer: B Explanation: Truffle is a comprehensive framework for Ethereum development. Question 16. What is the ERC-20 standard used for?
B) Cold wallet C) Paper wallet D) Web wallet Answer: B Explanation: Cold wallets, kept offline, reduce exposure to online threats. Question 20. What is the main purpose of the Hardhat framework? A) Mining blocks B) Smart contract development and testing C) Creating tokens D) Encrypting data Answer: B Explanation: Hardhat is a development environment for compiling, testing, and deploying smart contracts. Question 21. What does “public” modifier in Solidity function visibility mean? A) Only contract can call B) Only owner can call C) Any address can call D) Only derived contracts can call Answer: C Explanation: Public functions can be called externally and internally. Question 22. Why is collision resistance important in hash functions? A) Prevents duplicate transactions
B) Ensures different inputs produce unique outputs C) Increases mining speed D) Enables consensus Answer: B Explanation: Collision resistance ensures no two inputs have the same hash, securing data integrity. Question 23. Which protocol allows decentralized file storage for DApps? A) HTTP B) FTP C) IPFS D) SMTP Answer: C Explanation: IPFS is designed for decentralized storage and retrieval of files. Question 24. What is a “nonce” in the context of blockchain mining? A) Number of nodes B) Arbitrary number used once C) Network latency D) Type of address Answer: B Explanation: Nonce is a value miners increment to find a valid hash in Proof of Work. Question 25. What is the main benefit of using Hierarchical Deterministic (HD) wallets? A) Faster transactions B) Generate multiple addresses from a single seed
C) Integer Underflow D) Denial of Service Answer: A Explanation: Time-stamp dependence occurs when contracts rely on modifiable timestamps. Question 29. What is the role of oracles in smart contracts? A) Store contract code B) Connect blockchain to external data sources C) Mine blocks D) Generate wallets Answer: B Explanation: Oracles provide smart contracts with real-world data. Question 30. Which of the following describes Layer 2 scaling solutions? A) Network security enhancements B) Off-chain processing to improve scalability C) Additional consensus mechanisms D) Data encryption Answer: B Explanation: Layer 2 solutions process transactions off-chain, reducing main chain congestion. Question 31. What is a “channel” in Hyperledger Fabric? A) Network node B) Smart contract C) Private communication layer for specific members
D) Token standard Answer: C Explanation: Channels enable private transactions among a subset of network participants. Question 32. Which language is commonly used to write Hyperledger Fabric chaincode? A) Solidity B) Go C) Python D) C++ Answer: B Explanation: Chaincode is commonly written in Go, though Node.js and Java are also supported. Question 33. What is the purpose of the Membership Service Provider (MSP) in Hyperledger Fabric? A) Data encryption B) Identity management C) Token creation D) Network propagation Answer: B Explanation: MSP manages identities and access control in Fabric. Question 34. What does “Endorsement Policy” define in Hyperledger Fabric? A) Block generation time B) Number of nodes C) Which peers must validate a transaction D) Token supply
Explanation: Front-running involves exploiting transaction order for personal gain. Question 38. What is the primary function of MetaMask? A) Mining Ethereum B) Storing and interacting with Ethereum accounts via browser C) Creating NFTs D) Deploying Hyperledger chaincode Answer: B Explanation: MetaMask is a browser-based wallet for Ethereum and DApp interaction. Question 39. Which event keyword is used in Solidity to log data? A) require B) emit C) assert D) log Answer: B Explanation: The emit keyword is used to log events in Solidity. Question 40. What is the “Blockchain Trilemma”? A) Choosing between PoW and PoS B) Balancing decentralization, security, and scalability C) Hashing algorithm selection D) Token standard implementation Answer: B
Explanation: The trilemma refers to the difficulty in achieving all three: decentralization, security, scalability. Question 41. What is the role of Docker in Hyperledger Fabric network setup? A) Mining blocks B) Running nodes in isolated containers C) Encrypting data D) Generating wallets Answer: B Explanation: Docker containers enable easy setup and management of Fabric network components. Question 42. What is “Formal Verification” in smart contract development? A) Manual code review B) Mathematical proof of correctness C) Transaction mining D) Gas price estimation Answer: B Explanation: Formal verification uses mathematical methods to prove contract correctness. Question 43. Which process is responsible for grouping transactions into blocks in Hyperledger Fabric? A) Endorsing B) Ordering C) Validating D) Committing Answer: B
Explanation: State mutability indicates if a function can alter contract state. Question 47. What is the difference between “call” and “delegatecall” in Solidity? A) call executes code in caller’s context, delegatecall in callee’s B) delegatecall executes code in caller’s context, call in callee’s C) Both execute code in the same context D) Both are used for logging events Answer: B Explanation: delegatecall runs external contract code in the caller’s storage context. Question 48. What is “ABI” in Ethereum? A) Address Balance Index B) Application Binary Interface C) Account Blockchain Integration D) Automated Block Inclusion Answer: B Explanation: ABI defines how to encode/decode data to interact with smart contracts. Question 49. What is a “Testnet” used for in blockchain development? A) Mining real tokens B) Testing contracts without real assets C) Increasing block size D) Encrypting transactions Answer: B Explanation: Testnets allow developers to test applications without risking real assets.
Question 50. Which method is recommended for handling errors in Solidity? A) require(), revert(), assert() B) emit(), transfer(), call() C) if/else, loops D) delegatecall(), staticcall() Answer: A Explanation: These functions help handle errors and revert transactions as needed. Question 51. What is a “consortium blockchain”? A) Fully public blockchain B) Blockchain managed by a group of organizations C) Private blockchain for one company D) Permissionless blockchain Answer: B Explanation: Consortium blockchains are controlled collectively by multiple organizations. Question 52. Which property of blockchain enables transparency? A) Private key encryption B) Public ledger of transactions C) Hashing algorithms D) Token standards Answer: B Explanation: Transparency is achieved by recording transactions publicly.
A) Maximum block size B) Maximum computational effort allowed for a transaction C) Minimum transaction fee D) Number of tokens mined Answer: B Explanation: Gas limit defines the maximum computation allowed for a transaction. Question 57. What is the purpose of the “mapping” type in Solidity? A) Store sequential data B) Store key-value pairs C) Store only strings D) Store only integers Answer: B Explanation: Mapping is used for key-value storage in Solidity. Question 58. Which function in Solidity can be triggered when Ether is sent directly to a contract? A) fallback() B) receive() C) transfer() D) emit() Answer: B Explanation: receive() handles plain Ether transfers to contracts. Question 59. What is a “hot wallet”? A) Offline wallet
B) Online wallet for frequent transactions C) Hardware wallet D) Paper wallet Answer: B Explanation: Hot wallets are connected to the internet for easy access but less secure. Question 60. What does “staticcall” do in Solidity? A) Executes external contract code and allows state changes B) Executes code without allowing state changes C) Emits events D) Mines blocks Answer: B Explanation: staticcall allows calls to external contracts without modifying state. Question 61. What is the role of “Chainlink” in blockchain ecosystems? A) Token standard implementation B) Providing decentralized oracles C) Mining new blocks D) Generating wallets Answer: B Explanation: Chainlink offers decentralized data feeds for smart contracts. Question 62. What is “token allowance” in ERC-20? A) Total supply of the token B) Amount an address is permitted to spend on behalf of another
