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Blockchain Fundamentals & Architecture Flashcards

7 cards from real CCE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What is the primary purpose of a Merkle tree in a blockchain block?

    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.

  2. Which data structure does Ethereum use to store account state, enabling efficient updates and proofs?

    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.

  3. In the UTXO model used by Bitcoin, what does UTXO stand for?

    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.

  4. What happens to a blockchain when two miners simultaneously find valid blocks at the same height?

    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.

  5. What is a 'genesis block' in a blockchain?

    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.

  6. In a Proof-of-Work blockchain, what is a 'nonce'?

    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.

  7. Which property ensures that changing any data in a blockchain block invalidates all subsequent blocks?

    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.