Transactions & UTXO 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 has the worked format: a two-byte input script, one output with a one-byte script, and a total length of 63 bytes. Replace the input script with 254 bytes. All other fields are unchanged. What is the new total byte length?

2. A full transaction parses successfully but one byte remains after LockTime. What does DeserializeTx return?

Select one answer.

Success and ignore it Failure, because this API requires full consumption Success if the trailing byte is zero A transaction with one extra input

3. Which data does TxID hash in this exercise?

Select one answer.

The hexadecimal display string Only output amounts The canonical serialized transaction bytes, twice with SHA256 The previous transaction ID only

4. Available inputs are 11 and 6. A transaction consumes both and creates outputs 9 and 5. What is its fee? Enter a decimal integer.

5. A transaction lists the same available outpoint worth 7 twice and creates an output worth 13. What should happen?

Select one answer.

Accept with fee 1 Reject the duplicate input without changing state Accept if the scripts match Delete the input and then report a fee error

6. The first input exists but the second input is missing. What must ApplyTx preserve?

Select one answer.

Only the missing outpoint The entire original UTXO map Only transaction IDs, not values Nothing; partial consumption is allowed

7. Two individually valid transactions spend the same original outpoint. Why can a block not blindly accept both?

Select one answer.

Transaction IDs are always equal The second must validate against the state after the first consumed that output Coinbase must precede every ordinary transaction All blocks allow only one transaction

8. The isolated UTXO exercise accepts a zero-input coinbase. Does that prove its reward is valid for a block?

Select one answer.

Yes, any amount is valid Yes, if parsing succeeded No: subsidy and block fees are unavailable to this API No: coinbase can never have outputs

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