Unit 4: Ethereum blockchain and Distributed applications - Practice Quiz

1 Ethereum is best described as a blockchain platform that supports which key feature beyond simple value transfer?

2 Who is widely credited as the primary creator of Ethereum?

3 What is the native cryptocurrency of the Ethereum platform?

4 The smallest denomination of ether is known as:

5 What is the primary role of the Ethereum Virtual Machine (EVM)?

6 On the Ethereum network, the resource consumed to run computations on the EVM is called:

7 In Ethereum, which key must always be kept secret by the owner?

8 An Ethereum public key is mathematically derived from the:

9 A standard Ethereum address is how many hexadecimal characters long (excluding the "0x" prefix)?

10 An Ethereum address is typically derived from the last 20 bytes of the hash of the:

11 Which of the following is required to send a valid Ethereum transaction?

12 What field in an Ethereum transaction prevents the same transaction from being replayed?

13 In Ethereum, a message (internal transaction) is typically generated by a:

14 Unlike regular transactions, Ethereum messages are:

15 Which of the following is a well-known Ethereum test network?

16 Which tool is commonly used as a browser-based Ethereum wallet in the ecosystem?

17 A distributed application built on Ethereum is commonly abbreviated as:

18 Which language is most commonly used to write Ethereum smart contracts?

19 In a blockchain document verification DApp, what is usually stored on-chain instead of the full document?

20 In an Ethereum event registration DApp, smart contract "events" are mainly used to:

21 A developer wants a blockchain that supports Turing-complete smart contracts rather than just value transfers. Why is Ethereum preferred over Bitcoin for this purpose?

22 A team deploys and tests a contract without spending real funds before releasing it on the live chain. Which network should they use?

23 Which component of the Ethereum ecosystem allows a web application to interact with smart contracts from a browser?

24 In Ethereum, how is a public key mathematically derived from a private key?

25 An Ethereum address is derived by taking which portion of the Keccak-256 hash of the public key?

26 A user sends a transaction with a gas limit of 21000 and a gas price of 50 Gwei. What is the maximum fee they could pay?

27 In the EVM, what distinguishes a message (internal call) from a transaction?

28 A contract function requires a payment of 2 ether. How many wei must the caller send?

29 What is the primary role of gas in the Ethereum Virtual Machine?

30 During contract execution, if a transaction runs out of gas, what happens?

31 In a typical dApp architecture, where does the trusted, tamper-resistant business logic reside?

32 Why do dApps commonly use IPFS instead of storing large files directly in contract storage?

33 In an event-registration dApp, why are Solidity events emitted rather than returning data directly from a state-changing transaction?

34 An event-registration contract must prevent the same attendee from registering twice. Which approach best enforces this?

35 A document-verification dApp proves a file is authentic without storing the file on-chain. What is stored instead?

36 If even a single character in a verified document is altered, what happens when its hash is recomputed and compared to the stored hash?

37 A smart-contract call option gives the holder the right, but not the obligation, to buy an asset at a strike price. Which condition would a rational holder exercise it under?

38 Why is an oracle typically required when implementing a financial call option as a smart contract?

39 In an interest-rate swap implemented on-chain, two parties exchange cash flows. What is typically exchanged?

40 In an Industrial IoT scenario, how do sensor devices typically interact with an Ethereum smart contract?

41 A developer argues that Ethereum is fundamentally different from Bitcoin because it is "Turing-complete." Which consequence of this property is the primary reason Ethereum must impose a gas mechanism?

42 Two full nodes on the Ethereum mainnet temporarily disagree on the canonical chain head after receiving competing blocks at the same height. Under the fork-choice rule used post-Merge, which block becomes canonical?

43 A dApp team wants trust-minimized access to off-chain price data. Which ecosystem component addresses the "oracle problem," and what trade-off remains inherent to it?

44 Given an Ethereum private key , the public key is computed as on the secp256k1 curve. Why is recovering from considered computationally infeasible?

45 An Ethereum address is derived as the last 20 bytes of . What is the main security implication of truncating the 32-byte hash to 20 bytes?

46 After EIP-1559, a user sets maxFeePerGas = 100 gwei, maxPriorityFeePerGas = 2 gwei, and the block baseFee = 40 gwei. How much does the user pay per gas and how much is burned?

47 A transaction is stuck pending with nonce 5. To replace it, a user submits a new transaction. Which conditions make the replacement valid?

48 In EVM terminology, how does an internal "message" differ from an external transaction, and what key field is always absent in a message?

49 A contract function should receive plain ether transfers. Comparing transfer, send, and a low-level call, which statement reflects current best practice regarding the 2300 gas stipend?

50 A Solidity contract declares uint8 x = 255; x = x + 1; in a Solidity 0.7.x pragma without SafeMath. What is the resulting value of x and why?

51 Why does the EVM charge dramatically more gas for SSTORE (storage) than for operations on MSTORE (memory) within a single transaction?

52 A contract uses delegatecall to a library. In the called code, which execution context values refer to the calling contract rather than the library?

53 A dApp stores large user files on-chain by writing bytes to contract storage. An architect flags this as an anti-pattern. What is the correct remedy and the reason?

54 Consider a withdrawal function that sends ether before setting the user's balance to zero. Which attack does this enable and what is the standard mitigation?

55 An event-registration dApp emits Registered(address indexed user, uint256 timestamp). A frontend needs to efficiently query all registrations by a specific user. Which design choice makes this feasible and why?

56 A developer wants to use emitted events as the authoritative source of a contract's current state (e.g., "is user X registered now?"). Why is relying solely on events risky?

57 A document-verification contract stores Keccak256(document) on-chain. A user later proves authenticity by submitting the original document. Why does this scheme NOT guarantee the document existed before the on-chain record?

58 To verify a document belongs to a large registered set without storing all hashes on-chain, which structure lets a contract validate membership with a compact proof?

59 A smart contract implements a European call option on an ERC-20 asset with strike . At expiry the oracle price is . The holder should rationally exercise only when which condition holds, and the contract must guard against what?

60 An interest-rate swap smart contract settles floating-vs-fixed payments using IoT/industrial sensor-fed rate data pushed by field devices. Which combined risk must the design mitigate most carefully?