Question at position 18 Which of the following statements best describes a blockchain? (Choose the best answer.) A distributed, immutable ledger that records transactions across multiple nodes.An offline database system used for secure data storage.A network protocol used for email encryption.A centralized ledger controlled by a single entity.

Question

BlackTom AI · Accepted Answer

A blockchain is a distributed, immutable ledger that records transactions across multiple nodes.

1. Relevant knowledge points and concepts
- Distributed ledger: copies of the ledger exist on many network participants (nodes).
- Immutability: once blocks are appended, cryptographic hashing and consensus make altering past records unfeasible.
- Blocks and chaining: transactions are grouped into blocks; each block references the previous block’s hash, forming a chain.
- Consensus mechanisms (e.g., proof-of-work, proof-of-stake): ensure agreement among nodes about the ledger state.
- Decentralization and fault tolerance: no single controlling entity; resilience against single-point failures.

2. Complete reasoning process step by step
- Identify defining features: distributed copies, chain of hashed blocks, consensus to validate, tamper-evident history.
- Compare each option against those core features.
  a) “A distributed, immutable ledger that records transactions across multiple nodes.” Matches all core features.
  b) “An offline database system used for secure data storage.” Blockchain is typically online, networked, and not merely an offline secure database.
  c) “A network protocol used for email encryption.” Email encryption protocols (e.g., TLS, PGP) are different; blockchain is not an email protocol.
  d) “A centralized ledger controlled by a single entity.” Directly contradicts decentralization and distribution.

3. Intermediate steps / evidence
- Distributed copies: blockchains replicate state to participating nodes.
- Immutability: cryptographic hashes link blocks; altering one invalidates the chain.
- Transaction recording: every confirmed transaction is stored in blocks and visible to nodes (subject to permissions on private chains).

4. Why the correct answer is correct
The first option encapsulates the essential technical and architectural properties of blockchain: distribution across nodes, tamper-resistance via cryptographic linking, and transaction recording—precisely what blockchain technology provides.

5. Why other options are incorrect
- Option 2: mischaracterizes blockchain as offline and merely secure storage rather than a networked ledger with consensus.
- Option 3: confuses blockchain with communication/encryption protocols.
- Option 4: contradicts the decentralized nature; blockchains are designed to avoid single-entity control.

6. Conclusion
The correct choice is: "A distributed, immutable ledger that records transactions across multiple nodes." This matches the provided answer.

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