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PracticeUltimate Exam
Question 1. Which component of a blockchain block contains the hash of the previous block, thereby linking blocks together? A) Merkle Root B) Nonce C) Block Header D) Transaction List Answer: C Explanation: The block header includes the previous block’s hash, creating the immutable chain. Question 2. In a peer-to-peer (P2P) network, which topology allows each node to maintain a full copy of the ledger and broadcast new transactions to all peers? A) Star B) Mesh C) Tree D) Client-Server Answer: B Explanation: A mesh topology lets every node connect to many others, enabling full replication and gossip propagation. Question 3. What is the primary purpose of the Merkle Root in a block header? A) To store transaction fees B) To verify the integrity of all transactions in the block C) To determine the block difficulty D) To identify the miner’s address
PracticeUltimate Exam
Answer: B Explanation: The Merkle Root is a hash that summarizes all transaction hashes, allowing efficient integrity checks. Question 4. Which cryptographic primitive provides a one-way transformation used for proof-of-work mining? A) Symmetric encryption B) Digital signature C) Hash function D) Elliptic curve multiplication Answer: C Explanation: Hash functions like SHA-256 are computationally easy to compute but infeasible to reverse, forming the basis of PoW puzzles. Question 5. In Proof-of-Stake (PoS), what term describes the penalty imposed on a validator for malicious behavior? A) Burn B) Slashing C) Forking D) Staking Answer: B Explanation: Slashing destroys part or all of a validator’s staked tokens when they act against protocol rules. Question 6. Which consensus algorithm is classified as a Byzantine Fault Tolerant (BFT) protocol used primarily in permissioned blockchains? A) PoW B) Raft
PracticeUltimate Exam
A) Deploy a new contract B) Transfer Ether and invoke a function on another contract C) Halt execution D) Push a value onto the stack Answer: B Explanation: CALL sends Ether and executes code at a target address, enabling inter-contract communication. Question 10. Which of the following gas-related parameters protects the network from infinite loops in a transaction? A) Gas price B) Gas limit C) Gas refund D) Gas stipend Answer: B Explanation: The gas limit caps the maximum gas a transaction can consume; exceeding it aborts execution. Question 11. Which Solidity visibility modifier makes a function callable only from within the contract itself and its derived contracts? A) public B) private C) internal D) external Answer: C Explanation: internal restricts access to the contract and its children, but not external callers.
PracticeUltimate Exam
Question 12. In Solidity, which data type is best suited for storing a mapping from an address to a uint balance? A) array B) struct C) mapping D) enum Answer: C Explanation: mapping(address => uint) provides constant-time look-ups for balances. Question 13. Which global variable reflects the address that initiated the transaction, even if the call originated from a contract? A) msg.sender B) tx.origin C) block.coinbase D) address(this) Answer: B Explanation: tx.origin is the original external account that started the transaction chain. Question 14. Which ERC standard defines a multi-token interface that can represent both fungible and non-fungible tokens in a single contract? A) ERC- 20 B) ERC- 721 C) ERC- 1155 D) ERC- 777 Answer: C
PracticeUltimate Exam
D) Snapshot revert Answer: C Explanation: Ganache lets you set a custom block time to emulate realistic mining intervals. Question 18. Which library is primarily used to interact with Ethereum from a React front-end? A) Web3.py B) ethers.js C) BitcoinJS D) SolanaWeb3.js Answer: B Explanation: ethers.js offers a lightweight API for connecting wallets and sending transactions in JavaScript. Question 19. In MetaMask, what does the term “signer” refer to? A) The smart contract that validates a transaction B) The private key holder that produces a digital signature C) The node that mines a block D) The blockchain explorer that records signatures Answer: B Explanation: The signer uses the user’s private key to create a cryptographic signature for a transaction. Question 20. Which decentralized storage protocol uses content-addressed hashes to retrieve files, ensuring immutability? A) HTTP B) FTP
PracticeUltimate Exam
C) IPFS
D) S
Answer: C Explanation: IPFS stores data by its cryptographic hash, making the content immutable and verifiable. Question 21. What is a primary security risk when a smart contract directly trusts an off-chain price oracle without safeguards? A) Reentrancy B) Front-running C) Oracle manipulation D) Gas limit overflow Answer: C Explanation: If the oracle provides false data, the contract can be exploited for profit (e.g., price feed attacks). Question 22. Which static analysis tool can automatically detect reentrancy vulnerabilities in Solidity code? A) Truffle B) Slither C) Remix IDE D) Geth Answer: B Explanation: Slither performs symbolic analysis and flags common patterns like external calls before state updates. Question 23. In Solidity 0.8+, what happens when an arithmetic operation overflows?
PracticeUltimate Exam
Question 26. Which Layer-2 solution aggregates many transactions off-chain and posts a succinct proof to the main chain, guaranteeing correctness? A) Optimistic Rollup B) ZK-Rollup C) Sidechain D) Plasma Answer: B Explanation: ZK-Rollups generate zero-knowledge proofs that verify off-chain state transitions on-chain. Question 27. In an Optimistic Rollup, how are fraudulent state transitions prevented? A) By immediate zero-knowledge proofs B) By a challenge period where validators can submit fraud proofs C) By using a higher gas price D) By requiring all participants to run full nodes Answer: B Explanation: Optimistic Rollups assume correctness but allow anyone to challenge with a fraud proof during a set window. Question 28. Which Hyperledger Fabric component orders transactions and delivers them to peers? A) Peer B) Orderer C) Chaincode D) Channel Answer: B
PracticeUltimate Exam
Explanation: The Orderer service establishes total order of transactions before they are committed to ledgers. Question 29. In Hyperledger Fabric, what is the purpose of a “channel”? A) To store private keys B) To isolate ledger data among a subset of participants C) To execute smart contracts D) To broadcast events to the public network Answer: B Explanation: Channels create separate, permissioned ledgers visible only to authorized members. Question 30. Which consensus algorithm does Quorum use by default to achieve high throughput while preserving Ethereum compatibility? A) Raft B) Istanbul BFT (IBFT) C) PoW D) Tendermint Answer: B Explanation: Quorum’s default is Istanbul BFT, a permissioned BFT algorithm offering fast finality. Question 31. What is a “wrapped” asset in cross-chain communication? A) An on-chain token that represents an asset from another chain B) A token that has been burned C) A token with added metadata D) A token that cannot be transferred
PracticeUltimate Exam
C) Consortium board D) Miner council Answer: B Explanation: DAOs use token-based voting mechanisms to manage decisions without a central authority. Question 35. In Automated Market Makers (AMMs), what formula is commonly used to maintain constant product liquidity? A) x + y = k B) x * y = k C) x / y = k D) x² + y² = k Answer: B Explanation: The constant product invariant x * y = k underlies Uniswap-style AMMs, balancing token reserves. Question 36. Which DeFi primitive allows users to earn interest by supplying assets to a lending pool? A) Staking B) Yield farming C) Liquidity mining D) Lending pool (e.g., Compound) Answer: D Explanation: Lending protocols let users deposit assets and receive interest accrued from borrowers. Question 37. What is the primary benefit of using Self-Sovereign Identity (SSI) on blockchain?
PracticeUltimate Exam
A) Centralized control of user data B) Users own and control their identifiers without intermediaries C) Faster transaction confirmation D) Lower gas fees for identity verification Answer: B Explanation: SSI empowers individuals to manage their credentials directly, with cryptographic proofs stored on-chain. Question 38. Which cryptographic hash function is used by Ethereum for the Keccak-256 variant? A) SHA- 256 B) SHA-3 (Keccak) C) RIPEMD- 160 D) Blake2b Answer: B Explanation: Ethereum’s keccak256 is the Keccak-256 algorithm, a predecessor to the finalized SHA-3 standard. Question 39. In a permissioned blockchain, what role does a “certificate authority (CA)” play? A) Generates new blocks B) Issues digital certificates for node identities C) Executes smart contracts D) Manages token supply Answer: B Explanation: The CA signs X.509 certificates, enabling authenticated communication among authorized participants.
PracticeUltimate Exam
Explanation: storage variables are persisted in the contract’s state and occupy blockchain storage. Question 43. Which of the following is a key difference between ERC- 20 and ERC-777 token standards? A) ERC-777 introduces hooks for sending and receiving tokens B) ERC-777 removes the need for events C) ERC-20 supports batch transfers natively D) ERC-777 is not compatible with existing wallets Answer: A Explanation: ERC-777 adds tokensReceived and tokensToSend hooks, enabling richer interactions while remaining ERC-20 compatible. Question 44. What does the term “MEV” stand for, and why is it a concern for blockchain security? A) Minimum Execution Value; it limits gas price B) Miner Extractable Value; it enables profit from transaction ordering C) Multi-Entity Validation; it slows consensus D) Modular Encryption Vector; it weakens cryptography Answer: B Explanation: MEV refers to value miners (or validators) can capture by reordering, inserting, or censoring transactions, potentially harming fairness. Question 45. Which Ethereum improvement proposal introduced the concept of “EIP- 1559 ” and what does it primarily modify? A) Introduces a new consensus algorithm B) Changes gas pricing to include a base fee that is burned C) Adds a new opcode for randomness
PracticeUltimate Exam
D) Allows contracts to self-destruct Answer: B Explanation: EIP-1559 implements a dynamic base fee that is burned, making transaction fees more predictable. Question 46. In a DAO, what is a “snapshot” commonly used for? A) Recording the blockchain state for token voting power at a specific block B) Taking a picture of the network topology C) Backing up smart contract code D) Generating a new token distribution Answer: A Explanation: Snapshots capture token balances at a particular block to calculate voting rights, preventing manipulation after proposal creation. Question 47. Which layer-2 solution uses a “commit-chain” architecture where a separate validator set secures the child chain and periodically posts Merkle roots to Ethereum? A) Optimistic Rollup B) ZK-Rollup C) Plasma D) Sidechain (e.g., Polygon) Answer: C Explanation: Plasma chains submit periodic Merkle proofs to the root chain, enabling fast off-chain processing. Question 48. Which of the following best describes a “nonce” in the context of an Ethereum transaction? A) The transaction’s gas limit
PracticeUltimate Exam
A) The time it takes to mine a block B) The guarantee that a transaction cannot be reversed once confirmed C) The maximum block size D) The process of creating a new token Answer: B Explanation: Finality means the network has reached consensus such that the transaction is immutable. Question 52. Which of the following is a common method to mitigate front-running attacks in DeFi smart contracts? A) Using tx.origin for authentication B) Implementing commit-reveal schemes C) Increasing gas price dramatically D) Disabling events Answer: B Explanation: Commit-reveal separates intent submission from execution, preventing attackers from seeing and copying the transaction early. Question 53. What does the term “gas stipend” refer to in Ethereum? A) The extra gas automatically provided to a contract when receiving Ether via transfer B) The maximum gas a block can contain C) The gas price set by miners D) The amount of gas refunded after execution Answer: A Explanation: transfer and send forward 2300 gas to the recipient, enough only for a limited set of operations.
PracticeUltimate Exam
Question 54. Which Solidity data location is most gas-efficient for passing read-only arrays to external functions? A) storage B) memory C) calldata D) stack Answer: C Explanation: calldata is immutable and avoids copying data, making it cheaper for external function parameters. Question 55. In a Hyperledger Fabric network, what is the purpose of the “endorsement policy” for a chaincode? A) To define which orderer nodes can order transactions B) To specify which peers must sign a transaction proposal before it is considered valid C) To set the maximum transaction size D) To control token issuance Answer: B Explanation: Endorsement policies dictate which peers’ signatures are required for a transaction to be committed. Question 56. Which ERC standard introduces a standard interface for token royalties, enabling creators to receive a percentage on secondary sales? A) ERC- 20 B) ERC- 721 C) ERC- 2981 D) ERC- 1155
