A miner on a Proof-of-Work blockchain is trying to maximize revenue. The mempool contains a mix of high-fee and low-fee transactions. The block size limit is 1 MB. Which strategy should the miner use to assemble the most profitable block?

Include transactions based on their arrival time, prioritizing the oldest ones.

Include the highest-fee transactions first, filling the block to its size limit.

Include a random mix of transactions to ensure fairness across users.

Include only the lowest-fee transactions to encourage more users to transact.

Why might a developer choose to store data off-chain rather than on-chain?

To make the data visible to all network participants

To ensure the data is immutable and tamper-proof

To increase transaction throughput

To reduce storage costs and improve scalability

A blockchain network is under a spam attack. An attacker floods the mempool with thousands of low-fee transactions that are valid but never intended to be confirmed. The mempool is now full, and legitimate users are unable to get their transactions mined. What is the most effective mitigation that preserves the network's decentralization?

Increase the block size limit so more transactions can be included

Require all transactions to include a proof-of-work stamp

Implement a minimum fee threshold that all nodes enforce

Have miners prioritize transactions by fee rate and evict the lowest-fee transactions when the mempool is full

What happens to a transaction that fails validation on a node?

It is forwarded to other nodes for further validation

It is rejected and not included in the mempool or any block

It is sent back to the sender with an error code

It is stored in the mempool for later processing

What is the role of consensus in a blockchain network?

To ensure all nodes agree on the same valid blockchain state

To encrypt all transactions for privacy

To store transactions off-chain

To create new cryptocurrency tokens

EC-CouncilBlockchain Developer Certification

Domain 1Objective 4

Data and Transaction Flow in Blockchain BDC Practice Questions (Page 9)

Part of the Blockchain Fundamentals and Architecture domain, which makes up ~14% of our current practice bank.

51questions here

11free pages

10concepts

Questions 41–45

41expert · hard
A miner on a Proof-of-Work blockchain is trying to maximize revenue. The mempool contains a mix of high-fee and low-fee transactions. The block size limit is 1 MB. Which strategy should the miner use to assemble the most profitable block?
Select an answer first
42foundation · easy
Why might a developer choose to store data off-chain rather than on-chain?
Select an answer first
43expert · hard
A blockchain network is under a spam attack. An attacker floods the mempool with thousands of low-fee transactions that are valid but never intended to be confirmed. The mempool is now full, and legitimate users are unable to get their transactions mined. What is the most effective mitigation that preserves the network's decentralization?
Select an answer first
44foundation · easy
What happens to a transaction that fails validation on a node?
Select an answer first
45foundation · easy
What is the role of consensus in a blockchain network?
Select an answer first

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