Cryptocurrency Blockchain and Consensus Mechanisms 2

Question 1

What is a 51% attack in a proof-of-work blockchain?

Accepted Answer

When a single entity controls more than half the network's mining hash rate

Answer

A 51% attack occurs when one miner or pool controls the majority of hash rate, allowing them to rewrite recent transaction history.

Question 2

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

Accepted Answer

To efficiently summarize and verify all transactions in a block

Answer

A Merkle tree hashes transaction pairs recursively into a single Merkle root, enabling efficient and tamper-evident verification of any transaction.

Question 3

In Ethereum's proof-of-stake, what happens to a validator that behaves dishonestly?

Accepted Answer

Their staked ETH is partially or fully slashed

Answer

Slashing penalizes dishonest validators by destroying a portion of their staked ETH, making attacks financially costly.

Question 4

Which consensus property ensures that all honest nodes eventually agree on the same chain?

Accepted Answer

Agreement

Answer

Agreement (also called consistency) guarantees that all honest nodes converge on the same blockchain state.

Question 5

What distinguishes a hard fork from a soft fork?

Accepted Answer

Hard forks are backward-incompatible, splitting the chain if not universally adopted

Answer

A hard fork introduces rules that old nodes reject, potentially creating two separate chains if adoption is not unanimous.

Cryptocurrency Practice Test