Capstone Checkpoint

Trace exact representations and state, diagnose a failure, and return to its specific explanation.

Get every question correct to pass this checkpoint. You can review feedback, revise your answers, and submit again.

1. A transaction is admitted to the mempool. When are its inputs removed from the confirmed UTXO map?

Select one answer.

Immediately during admission When a valid winning block applies it When its fee is calculated When its txid is hashed

2. Two consecutive empty blocks use identical coinbase bytes. What can go wrong?

Select one answer.

SHA256 becomes reversible The second reward uses the same outpoint and overwrites an unspent reward Difficulty necessarily doubles The header has no timestamp

3. A block has subsidy 8 and ordinary transactions with fees 3 and 4. What is its maximum total coinbase value? Enter a decimal integer.

4. Why are all input ScriptSigs cleared when this capstone computes a signature digest?

Select one answer.

Scripts are never checked The digest must exclude the signature being constructed Output values do not matter It permits spending unknown outputs

5. A candidate B1 forks directly from genesis while A2 is active. Which view validates B1 inputs?

Select one answer.

A2, because it is currently active The mempool map only Genesis, because it is B1’s parent The view after applying B1 without checking

6. A valid side branch reaches the same height as the active branch. What does this course policy do?

Select one answer.

Replace the active tip automatically Delete the side branch Store it and retain the existing active tip Combine both UTXO maps

7. An actual coinbase is 21 bytes and a transaction is 62 bytes. The transaction-byte budget is 83. Which policy is correct?

Select one answer.

Reject because every coinbase reserves 100 bytes Include exactly; this capstone uses actual serialized sizes Exclude the coinbase from accounting Add another 80 header bytes to this budget

8. A caller provides a known header with changed transaction contents. What should ReceiveBlock do?

Select one answer.

Return true solely because its header ID is indexed Treat the contents as a mempool update Reject the body mismatch without state changes Skip Merkle commitments for all repeated blocks

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