Smart contracts run on:Traditional databasesCentralized serversBlockchainCloud platforms onlyC) BlockchainSmart contracts are self-executing programs stored on blockchain.
Which blockchain property ensures tamper-resistance?Distributed ledgerEncryptionConsensusHashingD) HashingEach block’s hash links it securely to the previous one.
Ethereum primarily uses which consensus mechanism (before ETH 2.0)?PoSPowPoaBFTB) PoWEthereum initially used Proof of Work before moving to Proof of Stake.
Which blockchain is permissioned and developed by IBM?EthereumHyperledger FabricCordaRippleB) Hyperledger FabricHyperledger Fabric is enterprise-focused with permissions.
In blockchain, “mining” refers to:Data storageValidating transactionsEncrypting dataDeleting blocksB) Validating transactionsMining secures transactions and adds blocks to the chain.
Which data structure is used in blockchain?ArrayLinked listHash chainQueueC) Hash chainEach block links to the previous one using cryptographic hashes.
Bitcoin uses which consensus mechanism?Proof of StakeProof of WorkByzantine Fault ToleranceDPoSB) Proof of WorkProof of Work requires solving puzzles to add new blocks.
A smart contract is:A contract written on paperCode that executes automaticallyA legal document stored digitallyA blockchain walletB) Code that executes automaticallySmart contracts are self-executing programs stored on blockchains.
Public blockchain is characterized by:Centralized authorityPermissionless accessRestricted participationHigh privacy onlyB) Permissionless accessAnyone can join and validate transactions in public blockchains.
Ethereum introduced:Distributed storageSmart contractsMining poolsBlockchain walletsB) Smart contractsEthereum was the first blockchain with built-in smart contract support.
The smallest unit of Bitcoin is called:BlockHash SatoshiTokenC) Satoshi1 Bitcoin = 100 million Satoshis.
Which cryptographic algorithm is used in Bitcoin?AESSHA-256MDSRSAB) SHA-256Bitcoin relies on SHA-256 hashing for security.
Forking in blockchain means:Splitting of chain into versionsCreating new walletsGenerating tokensMining new blocksA) Splitting of chain into versionsForks occur when blockchain protocols change, creating separate chains.
Permissioned blockchains are best for:Open cryptocurrencyPrivate enterprisesPeer-to-peer gamingPublic votingB) Private enterprisesPermissioned chains restrict access to known participants.
Smart contracts in Ethereum are written in:JavaSolidityPythonC++B) SoliditySolidity is Ethereum’s primary smart contract language.
Consensus mechanism ensures:Decentralized agreementDatabase replicationCentral controlPassword security onlyA) Decentralized agreementConsensus validates transactions without central authority.
Which blockchain introduced smart contracts?BitcoinEthereumRippleLitecoinB) EthereumEthereum allows programmable smart contracts.
A block contains:Hash, timestamp, transaction dataOnly transaction IDsOnly user credentialsPasswords onlyA) Hash, timestamp, transaction dataThese form the core structure of a blockchain block.
Mining in blockchain means:Storing filesValidating and adding transactionsEncrypting emailsFile compressionB) Validating and adding transactionsMining secures network and creates new blocks.
Proof-of-Stake differs from Proof-of-Work by:Using computational puzzlesUsing validators’ coin ownershipCentralized serversPassword sharingB) Using validators’ coin ownershipPoS selects validators based on stake in the network.
Which consensus algorithm is energy-efficient compared to PoW?PoSPoWDPoWSHA-256A) PoSProof-of-Stake uses validators instead of miners.
What ensures immutability in blockchain?Central serverChained hashesFirewallsSmart contractsB) Chained hashesEach block references the previous block’s hash.
Sidechains are used to:Replace public blockchainsEnable parallel transactions off main chainRemove minersStore backupsB) Enable parallel transactions off main chainSidechains scale blockchain by offloading operations.
Which cryptocurrency uses UTXO (Unspent Transaction Output) model?EthereumBitcoinRippleHyperledgerB) BitcoinBitcoin records transactions as UTXOs.
Smart contracts are written in which Ethereum language?JavaSolidityPythonScalaB) SoliditySolidity is Ethereum’s contract-oriented language.
Each block in a blockchain contains:Hash of the previous blockTransaction dataTimestampAll of theseD) All of theseEach block links with previous blocks using hashes, securing the chain.
Consensus algorithms ensure:Data duplicationAgreement among nodesFaster transactions onlyHash collisionsB) Agreement among nodesConsensus keeps all network nodes synchronized on blockchain state.
Proof of Stake” differs from “Proof of Work” by:Using computation instead of ownershipUsing ownership instead of computationIgnoring block validationIncreasing energy consumptionB) Using ownership instead of computationProof of Stake relies on validators’ staked coins, not power usage.
The blockchain’s immutability ensures:Records can’t be altered once addedNodes can delete dataAdmins can modify dataMiners can override blocksA) Records can’t be altered once addedCryptographic hashes prevent tampering.
The Merkle tree structure ensures:Fast hash collisionsEfficient block verificationToken issuanceSmart contractsB) Efficient block verificationMerkle trees enable quick integrity checks.
“Nonce” in mining means:Transaction fee Variable to find hash Private keySignatureB) Variable to find hashMiners adjust nonce until target hash is met.
Sidechains allow:Extra transactions without main chain loadCentral storage Consensus bypass Token burningA) Extra transactions without main chain loadThey extend blockchain functionality.
A 51% attack occurs when:Hackers own half the walletsOne entity controls majority hash powerNodes crashKeys expireB) One entity controls majority hash powerIt lets attackers alter transactions.
Public blockchains are characterized by:Restricted accessOpen participationPrivate keys onlyCentral authorityB) Open participationAnyone can join and validate transactions.
“Double spending” refers to:Mining two blocks simultaneouslySpending the same digital token twiceForking the chainHash duplicationB) Spending the same digital token twiceBlockchain prevents this via consensus and timestamps.
What is a block primarily composed of?CodeTransactionsWebsitesFilesB) TransactionsEach block contains a record of verified transactions.
What ensures immutability in blockchain?Central authorityHashingEncryption onlyTokensB) HashingCryptographic hashes make previous block changes detectable.
In Ethereum, what executes smart contracts?Blockchain NodesEVMTokensMiners onlyB) EVMThe Ethereum Virtual Machine processes and executes smart contracts.
What is “mining” in blockchain?Creating websitesValidating and adding blocksCopying dataDeleting old blocksB) Validating and adding blocksMining verifies transactions and secures the blockchain.
What type of blockchain is used within organizations?PublicConsortiumPrivateHybridC) PrivatePrivate blockchains restrict access to authorized users.
The first blockchain was introduced with which cryptocurrency?EthereumBitcoinRippleCardanoB) BitcoinBitcoin’s 2008 whitepaper introduced the concept of blockchain.
Smart contracts are primarily associated with:RippleEthereumBitcoinLitecoinB) EthereumEthereum allows automatic execution of smart contracts.
What is a “nonce” in blockchain mining?Transaction IDRandom number for hash Wallet addressPublic keyB) Random number for hashMiners adjust the nonce to find a valid block hash.
Bitcoin uses which consensus mechanism?Proof-of-StakeProof-of-WorkProof-of-AuthorityProof-of-ConceptB) Proof-of-Work PoW ensures miners solve cryptographic puzzles for block validation.
Blockchain stores data in:Hash tablesLinked blocksArrays QueuesB) Linked blocksEach block contains a hash that connects it to the previous block.
: A blockchain is a:Centralized databaseDistributed ledgerFile storageCloud serviceB) Distributed ledgerIt records transactions across multiple nodes securely.
Each block in a blockchain contains:Private key onlyData, hash, and previous hashSignature onlySingle transactionB) Data, hash, and previous hashLinking hashes ensures data integrity.
What is a smart contract?Digital agreement executed automaticallyTraditional agreementManual processDatabase transactionA) Digital agreement executed automaticallySmart contracts self-execute when conditions are met.
Blockchain ensures security primarily through:Central authorityCryptographyFirewallsCompressionB) CryptographyCryptographic hashing and digital signatures secure blockchain data.
Smart contracts execute automatically when:Network requestsConditions are metMiner signsManual triggersB) Conditions are metSmart contracts self-execute when coded rules are satisfied.
Consensus in blockchain ensures:Random validationAgreed ledger stateSingle mining nodeCloud storageB) Agreed ledger stateConsensus guarantees all nodes share a consistent record.
In blockchain, “nonce” refers to:Node nameOne-time random value for hashingDigital certificate Encryption keyB) One-time random value for hashingNonce changes input for proof-of-work calculations.
What type of blockchain uses a token to incentivize participation?PrivatePermissionedPublicFederatedC) PublicPublic blockchains like Bitcoin reward participants with tokens for validation work.
What is the purpose of a cryptographic nonce in blockchain mining?Encrypt walletsAdjust block hashTrack transactionsVerify smart contractsB) Adjust block hashA nonce is varied to produce a valid hash under network difficulty constraints.
Which consensus mechanism is most energy-efficient?Proof of WorkProof of StakeProof of AuthorityProof of BurnB) Proof of StakeProof of Stake replaces energy-intensive computations with staking-based validation.
What is the role of a “Merkle Tree”?Organize blockchain users Optimize smart contractsEfficiently verify data integrityEncrypt block headersC) Efficiently verify data integrityMerkle Trees store hashes of transactions, allowing efficient and secure verification.
What’s one limitation of blockchain scalability?Too many smart contractsLow transaction throughputLack of minersNo network accessB) Low transaction throughputDue to consensus and validation time, blockchains handle fewer transactions per second compared to centralized systems.
What structure does a blockchain primarily use to store data?Linked ListHash TableChain of BlocksGraphC) Chain of BlocksBlockchain organizes data in sequential, linked blocks secured by cryptography.
What is the purpose of a “nonce” in blockchain mining?To validate transactions To generate unique block hashTo link nodesTo encrypt dataB) To generate unique block hashThe nonce changes the hash value until it satisfies difficulty criteria.
Smart contracts execute:Legal documentsCode stored on blockchainMining operationsToken transfers onlyB) Code stored on blockchainSmart contracts are self-executing programs running on blockchain platforms.
Smart contracts are executed on which blockchain?BitcoinEthereumRipple Hyperledger onlyB) EthereumEthereum introduced smart contracts for decentralized automation.
The first block in blockchain is known as:Genesis BlockOrigin BlockRoot BlockInitial BlockA) Genesis BlockIt’s the first block of any blockchain chain.
Consensus mechanisms ensure:Data redundancyNetwork agreement on transactionsFaster miningHigher transaction feesB) Network agreement on transactionsConsensus ensures that all nodes validate transactions consistently.
What type of blockchain is used for business consortia?PrivatePublicConsortiumHybridC) ConsortiumConsortium blockchains allow multiple organizations to share control.
Hashing provides:EncryptionData linkage and integrityStorage optimizationKey distributionB) Data linkage and integrityHash functions ensure data integrity by producing unique, tamper-evident outputs.
Consensus mechanism ensures:Centralized controlAgreement among nodesUser authenticationEncryption onlyB) Agreement among nodeConsensus validates transactions collectively in blockchain.
Which of the following is a private blockchain platform?EthereumHyperledgerSolanaDogecoinB) HyperledgerHyperledger is a permissioned blockchain for enterprise use.