Blockchain Technology Smart Contract Fundamentals 4

Question 1

What is 'delegatecall' in Solidity, and why is it risky?

Accepted Answer

A low-level call that executes another contract's code in the calling contract's storage context

Answer

delegatecall runs the target's code but reads and writes the caller's storage slots, so a malicious or buggy implementation can corrupt or drain the proxy's state.

Question 2

In DeFi, what is a 'flash loan' and what makes it unique compared to traditional loans?

Accepted Answer

An uncollateralized loan that must be borrowed and repaid within a single transaction

Answer

Flash loans are uncollateralized because the smart contract enforces that the borrowed funds plus fee must be returned before the transaction finalizes, reverting everything if not.

Question 3

What does ERC-721 define, and how does it differ from ERC-20?

Accepted Answer

ERC-721 defines non-fungible tokens where each token has a unique ID; ERC-20 defines fungible tokens

Answer

ERC-721 tokens are non-fungible — each has a unique tokenId and is not interchangeable — whereas ERC-20 tokens are identical and interchangeable units.

Question 4

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

Accepted Answer

Inserting a transaction ahead of a pending one after observing it in the mempool to profit

Answer

Front-runners monitor the mempool, then pay a higher gas price to have their transaction mined first, exploiting information about a pending trade.

Question 5

What is the purpose of the 'selfdestruct' opcode in Solidity?

Accepted Answer

It permanently removes a contract's code and storage, sending its ETH balance to a specified address

Answer

selfdestruct deletes contract bytecode and storage from the Ethereum state and forcibly sends any remaining ETH to the target address, even if that address has no payable function.

Blockchain Practice Test

Blockchain Practice Test

Blockchain Technology Smart Contract Fundamentals 4