Blockchain Developer Core Blockchain Data Structures 2 — Questions and Answers
Question 1: In a Merkle tree, what is stored at each leaf node?
- The hash of an individual transaction (Correct answer)
- The block header
- A pointer to the previous block
- The nonce value
Correct answer: The hash of an individual transaction
Leaf nodes contain the hashes of individual transactions, which are then combined upward to form the Merkle root.
Question 2: What property of cryptographic hash functions ensures a tiny input change produces a completely different output?
- The avalanche effect (Correct answer)
- Collision resistance
- Determinism
- Preimage resistance
Correct answer: The avalanche effect
The avalanche effect means a single-bit input change cascades into a drastically different hash output.
Question 3: How does a block reference the block before it in the chain?
- By including the previous block's hash in its header (Correct answer)
- By storing the previous block's full data
- By using a sequential database ID
- By timestamp comparison
Correct answer: By including the previous block's hash in its header
Each block header contains the hash of the previous block, creating an immutable cryptographic link.
Question 4: What is the primary benefit of a Merkle tree for lightweight (SPV) clients?
- They can verify a transaction's inclusion without downloading the full block (Correct answer)
- They can mine blocks faster
- They eliminate the need for hashing
- They compress all transactions into one byte
Correct answer: They can verify a transaction's inclusion without downloading the full block
Merkle proofs let SPV clients confirm a transaction belongs to a block using only a small branch of hashes.
Question 5: If a Merkle tree has an odd number of leaf nodes, how is this commonly handled in Bitcoin?
- The last hash is duplicated to make a pair (Correct answer)
- The tree is rejected
- A zero hash is appended
- The odd node becomes the root directly
Correct answer: The last hash is duplicated to make a pair
Bitcoin duplicates the final hash when a level has an odd count so it can be paired and hashed.
Question 6: What data structure is a blockchain fundamentally based on?
- A hash-linked list of blocks (Correct answer)
- A balanced binary search tree
- A hash table
- A doubly-linked circular queue
Correct answer: A hash-linked list of blocks
A blockchain is essentially a singly-linked list where each node links backward via cryptographic hashes.
Question 7: Why is a blockchain considered tamper-evident?
- Altering one block changes its hash and breaks all subsequent links (Correct answer)
- Blocks are encrypted with private keys
- Miners manually inspect every block
- Each block has a digital watermark
Correct answer: Altering one block changes its hash and breaks all subsequent links
Changing any block's data invalidates its hash, which cascades and invalidates every later block's reference.
Blockchain Developer Core Blockchain Data Structures 2
In a Merkle tree, what is stored at each leaf node?