Ethereum Architecture and Transaction Lifecycle BBLC Practice Questions (Page 1)

Questions 1–5

1. 1application · medium

   A user submits a transaction to the Ethereum network. After a few seconds, the transaction appears in a block, but the block is not yet finalized. What does this mean for the transaction?

   • AThe transaction is invalid and will be removed from the block.
   • BThe transaction is still pending and has not been processed.
   • CThe transaction has been reverted and will not be executed.
   • DThe transaction is included in a block and will be executed, but finality is not yet guaranteed.
   Reveal Solution Discussion Select an answer first
2. 2application · medium

   A dApp needs to display a notification whenever a specific smart contract emits a 'Transfer' event. The frontend listens to the blockchain for these events. Which mechanism should the frontend use?

   • AQuery transaction receipts and parse the logs for the event signature.
   • BSubscribe to the contract's event logs via a WebSocket provider.
   • CMonitor the mempool for transactions that call the contract.
   • DPoll the contract's storage variables for changes.
   Reveal Solution Discussion Select an answer first
4. 3expert · hard

   A dApp needs to track every transfer of a specific ERC-20 token. The token contract emits a 'Transfer' event. The dApp's backend currently polls for new blocks and parses receipts. The team wants to reduce latency and avoid missing events. Which approach is most effective?

   • AUse a light node to filter events locally.
   • BSubscribe to the token contract's event logs via a WebSocket connection.
   • CIncrease the polling frequency to every block.
   • DMonitor the mempool for pending transactions that call the token contract.
   Reveal Solution Discussion Select an answer first
5. 4foundation · easy

   What is the primary use of logs (events) in Ethereum smart contracts?

   • ATo provide a way for off-chain applications to efficiently track and react to on-chain events
   • BTo encrypt transaction data for privacy
   • CTo store the contract's source code on-chain
   • DTo permanently store large amounts of data at low cost
   Reveal Solution Discussion Select an answer first
6. 5application · medium

   A smart contract function is called with a transaction that specifies a gas limit of 50,000. The function attempts to execute a loop that requires 60,000 gas. What will happen?

   • AThe transaction will succeed but the contract state changes will be discarded.
   • BThe transaction will succeed because the EVM will use the remaining gas from the block.
   • CThe transaction will be rejected during validation and never included in a block.
   • DThe transaction will run out of gas and be reverted, but the gas used will be charged.
   Reveal Solution Discussion Select an answer first