Quiz: What Is a Blockchain? 4 questions · 80% to pass 1. A blockchain is best described as:A single database stored on one company's serverA distributed ledger replicated across many nodes where entries cannot be altered once confirmedA type of cryptocurrencyAn encrypted email systemA blockchain is a distributed ledger maintained across a network of independent nodes. Once a transaction is confirmed through consensus, it becomes immutable. No single party can alter the record without the network detecting it.2. Immutability on a blockchain means:Transactions are instantOnce data is written and confirmed, it cannot be changed or deletedOnly the government can see the dataThe blockchain never goes offlineImmutability is the property that confirmed data cannot be retroactively altered. Each block references the previous block's hash, so changing any historical record would break the chain and be rejected by every other node in the network.3. Consensus mechanisms exist to:Speed up transactionsAllow nodes to agree on the valid state of the ledger without trusting a central authorityEncrypt user passwordsSet the price of a cryptocurrencyConsensus mechanisms (Proof of Work, Proof of Stake, Federated Consensus, etc.) solve the problem of getting independent, potentially adversarial nodes to agree on which transactions are valid without needing a trusted third party.4. A node in a blockchain network is:A physical coinA computer that maintains a copy of the ledger and participates in validating transactionsA wallet addressA type of smart contractNodes are the computers that make up the network. They store copies of the ledger, validate new transactions against the rules, and propagate valid transactions to other nodes. More nodes generally means more decentralization and security. Check answers Retake quiz Back to lesson Next lesson →