CCE Blockchain Fundamentals & Architecture 2 — Questions and Answers
Question 1: What is the primary purpose of a Merkle tree in a blockchain block?
- To store miner identity
- To efficiently verify transaction inclusion without downloading the full block (Correct answer)
- To encrypt the block header
- To determine block difficulty
Correct answer: To efficiently verify transaction inclusion without downloading the full block
Merkle trees allow lightweight clients to verify a transaction exists in a block using only a logarithmic number of hashes (Merkle proof), without downloading all transactions.
Question 2: Which data structure does Ethereum use to store account state, enabling efficient updates and proofs?
- Binary search tree
- Merkle Patricia Trie (Correct answer)
- Linked list
- Hash map
Correct answer: Merkle Patricia Trie
Ethereum uses a Merkle Patricia Trie (a combination of Merkle tree and Patricia trie) to store world state, allowing efficient updates and cryptographic proofs of account balances.
Question 3: In the UTXO model used by Bitcoin, what does UTXO stand for?
- Universal Token Exchange Output
- Unspent Transaction Output (Correct answer)
- Unified Transfer Exchange Operation
- Unrealized Token Exchange Option
Correct answer: Unspent Transaction Output
UTXO stands for Unspent Transaction Output — Bitcoin tracks balances as a set of unspent outputs rather than account balances, preventing double-spending.
Question 4: What happens to a blockchain when two miners simultaneously find valid blocks at the same height?
- Both blocks are discarded and a new round begins
- A temporary fork occurs and the chain with more cumulative work eventually wins (Correct answer)
- The block with the higher transaction fees is automatically selected
- The network halts until validators vote on which block to accept
Correct answer: A temporary fork occurs and the chain with more cumulative work eventually wins
A temporary fork (orphan/uncle situation) occurs; nodes follow the heaviest chain rule so the branch accumulating more proof-of-work is eventually accepted as canonical.
Question 5: What is a 'genesis block' in a blockchain?
- The block with the highest transaction volume
- The first block in the blockchain, hardcoded with no predecessor (Correct answer)
- The block that triggers a halving event
- The checkpoint block used for fast sync
Correct answer: The first block in the blockchain, hardcoded with no predecessor
The genesis block is block #0, hardcoded into the protocol with no parent hash — it is the immutable foundation from which all subsequent blocks chain.
Question 6: In a Proof-of-Work blockchain, what is a 'nonce'?
- A cryptographic signature used to authorize transactions
- An arbitrary number miners iterate to find a hash meeting the difficulty target (Correct answer)
- The timestamp embedded in each block
- The index number of a transaction within a block
Correct answer: An arbitrary number miners iterate to find a hash meeting the difficulty target
A nonce is a 32-bit number miners repeatedly change until the resulting block hash falls below the network's difficulty target.
Question 7: Which property ensures that changing any data in a blockchain block invalidates all subsequent blocks?
- Digital signature chaining
- Cryptographic hash chaining — each block contains the previous block's hash (Correct answer)
- Timestamping via a trusted authority
- Consensus voting by supermajority nodes
Correct answer: Cryptographic hash chaining — each block contains the previous block's hash
Because each block header includes the hash of the prior block, altering any block changes its hash, which breaks the link to the next block and propagates invalidation through the entire subsequent chain.
CCE Blockchain Fundamentals & Architecture 2
What is the primary purpose of a Merkle tree in a blockchain block?