Blockchain Technology Smart Contracts and dApps 4

Question 1

What is 'flash loan' arbitrage in DeFi?

Accepted Answer

Borrowing and repaying assets within a single transaction to profit from price differences

Answer

Flash loans allow uncollateralized borrowing within one atomic transaction; if not repaid with fees in the same block, the entire transaction reverts.

Question 2

Which tool is most commonly used to test Solidity smart contracts locally?

Accepted Answer

Hardhat or Foundry local development frameworks

Answer

Hardhat and Foundry provide local Ethereum node emulation, test runners, and debugging tools for smart contract development and testing.

Question 3

What is 'front-running' in the context of Ethereum smart contracts?

Accepted Answer

Inserting a transaction ahead of a known pending transaction to profit from it

Answer

Front-running occurs when a miner or bot spots a profitable pending transaction in the mempool and submits their own transaction with higher gas to execute first.

Question 4

In Solidity, what does the 'modifier' keyword allow developers to do?

Accepted Answer

Reuse pre- and post-condition checks across multiple functions

Answer

Modifiers wrap functions with reusable logic (e.g., access checks), using the '_' placeholder to indicate where the modified function's body executes.

Question 5

What is the 'Merkle tree' used for in the context of smart contracts and NFT whitelists?

Accepted Answer

Efficiently verifying membership in a large set without storing the full list on-chain

Answer

A Merkle tree allows a contract to verify whether an address is in a whitelist by checking a small proof against a root hash stored on-chain, saving gas.

Blockchain Practice Test

Blockchain Practice Test

Blockchain Technology Smart Contracts and dApps 4