Ethereum Smart Contracts BBLC Practice Questions (Page 6)

Questions 26–30

1. 26foundation · easy

   Why is gas used in Ethereum smart contracts?

   • ATo provide a reward for users who hold Ether in their wallets.
   • BTo prevent infinite loops and ensure that computational resources are fairly compensated.
   • CTo encrypt the data stored on the blockchain.
   • DTo enable smart contracts to communicate with external APIs.
   Reveal Solution Discussion Select an answer first
2. 27foundation · easy

   Which of the following lists the stages of a smart contract's lifecycle in the correct order?

   • ADeployment, creation, execution, self-destruction
   • BSelf-destruction, deployment, creation, execution
   • CCreation, deployment, execution, self-destruction
   • DExecution, creation, deployment, self-destruction
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4. 28application · medium

   A company deployed a smart contract to manage a loyalty points system. After a merger, they need to completely remove the contract and its data from the Ethereum blockchain. What is the only way to achieve this?

   • AUse a special 'delete' opcode from within the contract to clear its own storage.
   • BAsk the Ethereum foundation to remove the contract from the blockchain.
   • CSend a transaction to the contract address with no data to trigger a fallback function that deletes the contract.
   • DCall the selfdestruct function in the contract, which sends any remaining Ether to a designated address and removes the code and storage.
   Reveal Solution Discussion Select an answer first
5. 29application · medium

   A startup is deploying a Solidity smart contract to Ethereum mainnet. They want to minimize deployment cost while ensuring the contract can be upgraded later. Which approach should they take?

   • ADeploy the contract with a selfdestruct function that can be called by the owner to remove the code and free up gas.
   • BDeploy a proxy contract that delegates calls to an implementation contract, and update the proxy's address when needed.
   • CDeploy the contract with all functions marked as payable to reduce the gas cost of future transactions.
   • DDeploy the contract to a private blockchain and later migrate the state to mainnet using a migration tool.
   Reveal Solution Discussion Select an answer first
6. 30application · medium

   A user is sending a transaction to a smart contract that will update a state variable from 0 to 1. They notice that the gas cost is higher than expected. Which factor is most likely causing the higher cost?

   • AThe transaction is writing to a storage slot for the first time, which costs more gas than updating an existing value.
   • BThe transaction is being sent during a period of high network congestion.
   • CThe transaction is using a memory variable instead of a storage variable.
   • DThe transaction is calling a view function that reads the state.
   Reveal Solution Discussion Select an answer first