Bitcoin Network and Its Transactions BDC Practice Questions (Page 8)

Questions 36–40

1. 36application · easy

   A user has a UTXO of 1 BTC and wants to send 0.6 BTC to a merchant. The user's wallet creates a transaction with one input (1 BTC) and two outputs: 0.6 BTC to the merchant and 0.39 BTC as change. What is the transaction fee?

   • A0.39 BTC
   • B0.6 BTC
   • C0 BTC
   • D0.01 BTC
   Reveal Solution Discussion Select an answer first
2. 37expert · hard

   A node receives a block that contains a transaction spending a UTXO that the node has already seen spent in a different transaction in the same block. The node is validating the block. What should the node do?

   • AAccept the block and mark the second transaction as invalid, but keep the block.
   • BAccept the block because the transactions are in the same block and the UTXO is spent only once.
   • CReject the block because it contains a double-spend.
   • DAccept the block and remove the UTXO from the UTXO set after the first transaction.
   Reveal Solution Discussion Select an answer first
4. 38application · medium

   A user broadcasts a Bitcoin transaction and receives a transaction ID. The transaction is not yet confirmed. What does the transaction ID represent?

   • AThe hash of the transaction data, which can change if the transaction is modified.
   • BThe unique identifier assigned by the first node that received the transaction.
   • CThe block hash in which the transaction will be included.
   • DThe digital signature of the transaction.
   Reveal Solution Discussion Select an answer first
5. 39expert · hard

   A user creates a Bitcoin transaction and signs it. Before broadcasting, the user realizes that the fee is too low and wants to increase it. The transaction has not been broadcast yet. What is the most efficient way to increase the fee?

   • ARebroadcast the same transaction after modifying the fee field in the raw transaction.
   • BBroadcast the original transaction and then use RBF to replace it.
   • CCreate a new transaction that spends the same inputs but with a lower change output, and sign it again.
   • DAdd a new input to the transaction and sign it, without changing the outputs.
   Reveal Solution Discussion Select an answer first
6. 40application · medium

   A developer is debugging a transaction that was rejected by the network. The transaction spends a P2PKH output. Which of the following is a valid reason for rejection?

   • AThe transaction uses a change address that is different from the sender's address.
   • BThe transaction fee is exactly the minimum relay fee.
   • CThe transaction has a locktime in the past.
   • DThe public key provided in the input does not hash to the address in the output script.
   Reveal Solution Discussion Select an answer first