CCE Blockchain Fundamentals 3 — Questions and Answers
Question 1: What is a 51% attack in blockchain networks?
- When 51% of nodes upgrade to a new protocol version
- When an entity controls the majority of network hash rate and can double-spend (Correct answer)
- When a block contains more than 51% unconfirmed transactions
- When staking rewards are reduced by 51% during a halving event
Correct answer: When an entity controls the majority of network hash rate and can double-spend
A 51% attack occurs when a single miner or pool controls over half the hash rate, enabling them to rewrite recent blocks and potentially double-spend coins.
Question 2: Which data structure does a blockchain most closely resemble?
- Hash table
- Binary search tree
- Singly linked list (Correct answer)
- Circular queue
Correct answer: Singly linked list
A blockchain is structurally a linked list where each block contains a cryptographic reference (hash) to its predecessor.
Question 3: What is 'sharding' designed to solve in blockchain systems?
- Private key exposure during wallet recovery
- Double-spending in zero-confirmation transactions
- Scalability bottlenecks by partitioning the network into parallel subsets (Correct answer)
- High mining energy consumption
Correct answer: Scalability bottlenecks by partitioning the network into parallel subsets
Sharding splits the blockchain network into smaller partitions (shards) that process transactions in parallel, increasing overall throughput.
Question 4: In proof-of-stake consensus, what primarily determines a validator's chance of proposing the next block?
- The speed of the validator's internet connection
- The amount of cryptocurrency the validator has staked (Correct answer)
- The validator's geographic location
- The age of the validator's node software version
Correct answer: The amount of cryptocurrency the validator has staked
In PoS, validators are selected to propose blocks proportionally to the amount of cryptocurrency they have locked as collateral (stake).
Question 5: What is a blockchain 'oracle'?
- A node that stores only block headers
- A smart contract that auto-executes on a fixed schedule
- A service that feeds real-world data to on-chain smart contracts (Correct answer)
- A consensus mechanism used in private blockchains
Correct answer: A service that feeds real-world data to on-chain smart contracts
Oracles bridge the gap between blockchains and external data sources, supplying smart contracts with off-chain information like prices or event outcomes.
Question 6: What is the purpose of the 'difficulty adjustment' mechanism in Bitcoin?
- To increase block size when network traffic is high
- To keep average block production time near 10 minutes despite changing hash rate (Correct answer)
- To reduce transaction fees during periods of low demand
- To limit the number of nodes allowed to participate in consensus
Correct answer: To keep average block production time near 10 minutes despite changing hash rate
Bitcoin recalculates mining difficulty every 2016 blocks to maintain an approximately 10-minute block interval regardless of total network hash power.
Question 7: Which property ensures that altering any block in a blockchain invalidates all subsequent blocks?
- Digital signatures on each transaction
- Each block's hash is included in the next block's header (Correct answer)
- Timestamps are enforced by a central authority
- All nodes vote on block validity in real time
Correct answer: Each block's hash is included in the next block's header
Because each block header contains the previous block's hash, modifying one block changes its hash and breaks the chain link to every following block.
CCE Blockchain Fundamentals 3
What is a 51% attack in blockchain networks?