Blockchain Pedagogy

Courses

Course 4: Blockchain Systems, Consensus & Scalability – Quiz

Select the correct answer mentally or on paper. Answers are provided at the end for self-checking.

1. What is the primary purpose of consensus in a blockchain network?

  • A. To reduce transaction fees
  • B. To ensure all nodes agree on a single canonical history
  • C. To increase block size
  • D. To generate smart contracts automatically

2. Nakamoto consensus achieves security primarily through:

  • A. Bandwidth allocation
  • B. Proof-of-work difficulty adjustments
  • C. Token staking rewards
  • D. Zero-knowledge proofs

3. In Proof-of-Stake, validator selection is proportional to:

  • A. CPU cores
  • B. Amount of staked capital
  • C. Number of transactions sent
  • D. Block timestamps

4. Which model represents state using discrete spendable objects?

  • A. Account-based model
  • B. UTXO model
  • C. Plasma state model
  • D. Rollup state representation

5. In Merkle trees, a Merkle proof grows in size proportional to:

  • A. Total number of nodes
  • B. Logarithm of number of leaves
  • C. Square root of transaction count
  • D. Total block height

6. LMD-GHOST is used to determine:

  • A. Gas fees
  • B. The heaviest supported blockchain branch
  • C. Smart contract execution order
  • D. Transaction compression

7. BFT consensus generally requires n ≥ 3f + 1. Here, f refers to:

  • A. Network latency factor
  • B. Faulty or malicious nodes
  • C. Fee-paying users
  • D. File storage capacity

8. Deterministic finality means that:

  • A. Blocks can be reverted only if extremely improbable lottery events occur
  • B. Once finalised, a block cannot be reverted unless >â…“ validators misbehave
  • C. Forks never occur
  • D. Fee markets remain stable

9. Sharding improves scalability by:

  • A. Increasing gas fees
  • B. Reducing total number of nodes
  • C. Partitioning workload across multiple validator subsets
  • D. Running PoW and PoS together

10. Cross-shard communication is challenging because:

  • A. Shards cannot be synchronised
  • B. Messages may require proofs, ordering, and coordination across partitions
  • C. Each shard uses a different programming language
  • D. Users cannot send transactions across shards

11. Data Availability Sampling (DAS) helps ensure that:

  • A. Validators have unlimited storage
  • B. Light clients can verify block data without downloading everything
  • C. Every shard implements PBFT
  • D. Block producers cannot propose invalid fees

12. DAG-based blockchain architectures allow:

  • A. Only one block to be produced at a time
  • B. Multiple blocks to be produced concurrently
  • C. Smart contracts to execute automatically
  • D. Rollups to operate on Layer 1

13. Stateless clients rely on:

  • A. Storing full on-chain state locally
  • B. Witness proofs (e.g., Merkle/Verkle proofs)
  • C. Consensus-time checkpoints only
  • D. Archival node snapshots

14. Payment channels require users to:

  • A. Download full blockchain history
  • B. Lock funds in a channel-opening transaction
  • C. Submit every transfer on-chain
  • D. Trust a federation

15. In optimistic rollups, correctness is enforced by:

  • A. Zero-knowledge proofs
  • B. Fraud proofs during challenge windows
  • C. Native PoW validators
  • D. Multi-chain lotteries

16. ZK rollups differ from optimistic rollups in that they:

  • A. Require trust in sequencers
  • B. Provide cryptographic validity proofs
  • C. Cannot process transactions off-chain
  • D. Always rely on fraud proofs

17. Cross-chain bridges are considered high risk because:

  • A. They reduce block size
  • B. A compromised bridge can mis-account or steal locked assets
  • C. They slow down consensus dramatically
  • D. They disable Layer 2 systems

18. A major limitation of BFT protocols is:

  • A. They cannot run on PoS networks
  • B. Their O(n²) communication overhead at large validator counts
  • C. They require mining hardware
  • D. They cannot finalise blocks

19. Propagation optimisations such as compact blocks help by:

  • A. Lowering user gas fees
  • B. Reducing wasted bandwidth and decreasing fork rates
  • C. Eliminating mempools
  • D. Preventing block proposals

20. Full blockchain scalability typically requires:

  • A. Only Layer 1 optimisation
  • B. Only Layer 2 rollups
  • C. A combination of L1 improvements and L2 scaling strategies
  • D. Removing consensus entirely

Answer Key

  1. 1: B
  2. 2: B
  3. 3: B
  4. 4: B
  5. 5: B
  6. 6: B
  7. 7: B
  8. 8: B
  9. 9: C
  10. 10: B
  11. 11: B
  12. 12: B
  13. 13: B
  14. 14: B
  15. 15: B
  16. 16: B
  17. 17: B
  18. 18: B
  19. 19: B
  20. 20: C

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