Data and Transaction Flow in Blockchain BDC Practice Questions (Page 8)

Questions 36–40

1. 36expert · hard

   A developer is designing a custom blockchain and wants to prioritize transactions in the mempool based on the fee-to-size ratio. Which data structure is most appropriate for this purpose?

   • ABinary search tree
   • BLinked list
   • CPriority queue
   • DHash map
   Reveal Solution Discussion Select an answer first
2. 37expert · hard

   A consortium blockchain uses a delegated proof-of-stake (DPoS) consensus with a fixed set of 21 block producers. A developer argues that transactions on this network achieve absolute finality after one block because the block producers are known and the chain does not fork. Is this argument valid?

   • AYes, because DPoS does not allow forks
   • BNo, because DPoS is not a real consensus algorithm
   • CYes, because the block producers are trusted
   • DNo, because finality depends on the consensus protocol's rules, not just the number of producers
   Reveal Solution Discussion Select an answer first
4. 38application · easy

   A node receives a transaction that spends a UTXO which was already spent in a transaction included in a previous block. What should the node do?

   • AReject the transaction as invalid because it attempts a double-spend
   • BAdd it to the mempool and wait for the next block
   • CAccept it if the fee is higher than the original transaction
   • DForward it to peers to see if they accept it
   Reveal Solution Discussion Select an answer first
5. 39foundation · easy

   Which of the following is an example of off-chain data in a blockchain application?

   • AThe timestamp of a block
   • BThe transaction amount in a cryptocurrency transfer
   • CThe full contents of a large file stored in a distributed storage system like IPFS
   • DThe hash of a document stored in a smart contract
   Reveal Solution Discussion Select an answer first
6. 40application · medium

   A user submits a transaction to a public blockchain node. The node checks the signature, confirms the inputs are unspent, and verifies the fee is sufficient. The node then adds the transaction to its local mempool and relays it to peers. Which additional validation step must the node perform before the transaction is considered valid for inclusion in a block?

   • ACheck that the transaction's output script matches the recipient's public key hash
   • BVerify that the transaction's locktime has not expired
   • CConfirm that the transaction is not a double-spend of any input already in the mempool
   • DWait for the transaction to be included in a block before relaying it
   Reveal Solution Discussion Select an answer first