Bitcoin Blockchain Architecture BBLC Practice Questions (Page 5)

Questions 21–25

1. 21application · medium

   A Bitcoin wallet developer is debugging a transaction that failed to broadcast. The transaction spends a UTXO of 0.5 BTC and creates two outputs: 0.3 BTC to a recipient and 0.2 BTC as change. The developer notices that the transaction fee is 0.0001 BTC. Why might the transaction be rejected by full nodes?

   • AThe change output of 0.2 BTC is too large and violates the dust limit.
   • BThe sum of the outputs (0.5 BTC) equals the input, leaving no fee for miners.
   • CThe recipient output of 0.3 BTC exceeds the maximum allowed transaction output.
   • DThe transaction uses two outputs, which is not allowed in a standard transaction.
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2. 22expert · hard

   A Bitcoin miner is considering whether to include a transaction with a very low fee in the next block. The mempool is not congested, and the miner has plenty of block space. Which decision is most rational for the miner?

   • AInclude the transaction because the miner can collect the fee without displacing higher-fee transactions, and the block is not full.
   • BExclude the transaction because low-fee transactions are always invalid and will be rejected by the network.
   • CInclude the transaction only if the sender increases the fee to the network's minimum.
   • DExclude the transaction because including it would reduce the block reward.
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4. 23foundation · easy

   Which property of the Bitcoin blockchain ensures that once a transaction is recorded, it cannot be easily altered?

   • AScalability
   • BAnonymity
   • CInteroperability
   • DImmutability
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5. 24application · medium

   A miner is trying to find a valid block. The miner has a set of pending transactions and a candidate block header. Which action does the miner take to find a valid block?

   • AThe miner adds more transactions to the block to increase the chance of finding a valid hash.
   • BThe miner waits for the network to provide a valid nonce, then includes it in the block.
   • CThe miner repeatedly changes the nonce in the block header and hashes it until the hash is below the current difficulty target.
   • DThe miner changes the timestamp in the block header to a future date to make the hash valid.
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6. 25application · medium

   A blockchain educator is teaching a class about Bitcoin's structure. A student asks: 'Why is the genesis block special?' Which answer is most accurate?

   • AIt is the only block that does not require proof-of-work.
   • BIt is the first block in the chain and has no previous block hash, so it is hardcoded into the Bitcoin software.
   • CIt is re-mined every time the network restarts, which is why it is called the genesis block.
   • DIt contains the largest block reward ever mined, which is why it is so valuable.
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