Unit 6: Ethereum, Web3 and Decentralized Applications - Practice Quiz

1 What is Ethereum primarily designed to support?

2 What is the native cryptocurrency of Ethereum?

3 What type of network is the Ethereum mainnet?

4 Which component allows a user to manage Ethereum accounts and sign transactions?

5 What is the main purpose of the Ethereum Virtual Machine (EVM)?

6 What does gas measure in an Ethereum transaction?

7 What is a smart contract?

8 What usually triggers the execution of an Ethereum smart contract function?

9 Which tool provides a browser-based environment for writing and testing Solidity contracts?

10 What does an Ethereum block contain?

11 Which item must a wallet owner keep secret?

12 Which of the following is an Ethereum execution client?

13 What is a basic function of an Ethereum node?

14 Who proposes blocks on Ethereum mainnet after its transition to proof of stake?

15 Which API style is commonly used to communicate with an Ethereum node?

16 What is a decentralized application (DApp)?

17 What does the Ethereum Name Service (ENS) provide?

18 Which programming language is widely used to write Ethereum smart contracts?

19 What is created when a smart contract is successfully deployed to Ethereum?

20 Which Geth command is commonly used to connect a console to a running Geth node?

21 A user wants an Ethereum account that can initiate transactions directly using a private key. Which type of account should be used?

22 A signed transaction intended for one Ethereum-compatible network should not be replayed on another network. Which transaction field primarily provides this protection?

23 A frontend application has a deployed contract address but cannot correctly encode calls to its functions. Which additional artifact does it most directly need?

24 A contract function runs out of gas after changing a state variable but before execution completes. What is the expected result?

25 A withdrawal function sends Ether to a user before reducing the user's recorded balance. Which vulnerability is most likely?

26 A developer needs fast, repeatable contract tests with controllable accounts and no real transaction fees. Which environment is most suitable?

27 A DApp waits for several additional blocks after a transaction is included before treating it as reliable. What risk is this practice mainly intended to reduce?

28 A DApp asks a browser wallet to send a transaction. Which operation should normally remain inside the wallet?

29 On Ethereum's current proof-of-stake network, which participant is responsible for proposing blocks in assigned slots?

30 A DApp needs to read a contract's current value without creating a transaction or changing blockchain state. Which JSON-RPC method is most appropriate?

31 A DApp dashboard must update when a contract emits a Transfer event. Which data source should the frontend monitor?

32 A DApp must distribute a large document without storing the entire file in expensive contract storage. Which approach is most appropriate?

33 After compiling a Solidity contract, which pair of outputs is most useful for deployment and frontend interaction?

34 A contract constructor fails a require condition during deployment. What should the developer expect?

35 After attaching to a running Geth JavaScript console, which expression can be used to inspect the latest block number known to the node?

36 A script is preparing several transactions from the same account. Which Web3 query best helps choose a nonce that includes already pending transactions?

37 A client receives a transaction hash immediately after broadcasting a transaction. What should it check to confirm that the transaction was included and whether execution succeeded?

38 A Solidity function needs a temporary array only while the current external call is executing. Which EVM data area is generally appropriate?

39 A contract must settle an insurance claim using rainfall measured in the physical world. Why is an oracle needed?

40 An offline wallet has already signed and serialized an Ethereum transaction. Which JSON-RPC method should be used to broadcast it?

41 An EOA has confirmed nonce . It broadcasts two otherwise valid transactions: transaction with nonce reaches a node before transaction with nonce . What is the most accurate expected behavior?

42 Two EVM-compatible networks accidentally use the same EIP-155 chain ID. An account has matching nonce and sufficient funds on both networks. Which consequence is most relevant?

43 After Ethereum's transition to proof of stake, a non-validating full node runs only an execution client and has no consensus client connected through the Engine API. What critical capability is missing?

44 A contract copies a large slice of transaction calldata into previously unused memory and then hashes it. Which statement best describes the EVM effects?

45 Contract changes its own storage and then makes a low-level call to contract . Contract changes storage but executes REVERT; checks the returned status and continues successfully. What is the resulting state?

46 A withdrawal function reads balances[msg.sender], sends Ether using call, and only afterward sets the balance to zero. Which modification most directly addresses the reentrancy vulnerability without relying solely on gas stipends?

47 An upgradeable proxy uses DELEGATECALL. A new implementation changes the order and types of state variables, after which balances appear corrupted. Which EVM property explains this result?

48 A test suite forks Ethereum at a fixed historical block and all integration tests pass. The deployed DApp later fails because an oracle's current state differs from its state at the fork block. What conclusion is justified?

49 Under EIP-1559, suppose a block uses exactly twice its gas target, which is also the protocol's maximum block gas usage. Ignoring integer rounding, how does the next block's base fee change?

50 A DApp observes a successful receipt and immediately treats its event as irreversible. A short chain reorganization then removes the containing block. Which interpretation is correct?

51 A user broadcasts two EIP-1559 transactions from one account with the same nonce but different recipients. The second satisfies the client's replacement-fee rules. What outcome should the wallet expect?

52 A hardware wallet is used with an untrusted remote Ethereum node. Which workflow best preserves the wallet's key-isolation guarantee?

53 Which description accurately reflects block production on post-merge Ethereum?

54 A write operation simulated with eth_call at the latest block returns success, but the same signed transaction later reverts after inclusion. Which explanation is most accurate?

55 Solidity emits event Registered(string indexed name, uint256 value). A client receives only the log topics and data. What can it determine about name without an external candidate set?

56 A DApp indexes logs and must remain correct across short reorganizations. Which design is most robust?

57 A smart contract stores an IPFS CID for a DApp asset. Months later, no IPFS node retains the corresponding content. Which statement is correct?

58 A Solidity contract authorizes operations using keccak256(abi.encodePacked(a, b)), where both a and b are user-controlled strings. What is the main risk and appropriate correction?

59 A factory deploys contracts with CREATE2. Which expression determines the deployed address, and what implication follows for constructor arguments?

60 Two independent services connected to the same Geth node each query eth_getTransactionCount(address, "pending") simultaneously and receive nonce . Both then sign different transactions with nonce . What is the best remedy?