CCE Smart Contracts and Ethereum 2

Question 1

What does the ERC-20 token standard define?

Accepted Answer

A common set of rules for creating interchangeable (fungible) tokens on Ethereum

Answer

Rules for creating unique non-fungible tokens on Ethereum

Answer

The protocol governing how Ethereum nodes reach consensus

Answer

Standards for creating multi-signature wallet contracts on Ethereum

Question 2

What is the key difference between an Externally Owned Account (EOA) and a contract account in Ethereum?

Accepted Answer

EOAs are controlled by a private key; contract accounts are controlled by smart contract code

Answer

EOAs have larger on-chain storage capacity than contract accounts

Answer

Contract accounts are controlled by a private key; EOAs are controlled by code

Answer

There is no functional difference — both types can be used interchangeably

Question 3

What is a 'reentrancy attack' in the context of smart contracts?

Accepted Answer

An attack where a malicious contract calls back into the victim contract before the first execution completes

Answer

Repeatedly broadcasting the same signed transaction to drain gas fees

Answer

A method to bypass access control by re-registering a contract at a previously used address

Answer

An exploit that prevents a smart contract from ever being called again

Question 4

What does the 'payable' keyword do in a Solidity smart contract?

Accepted Answer

It allows a function or address to receive Ether as part of a transaction

Answer

It makes the function free to call by waiving the gas requirement

Answer

It automatically sends Ether to the contract owner after every call

Answer

It restricts a function so only verified payment processors can call it

Question 5

What is the primary purpose of events in Ethereum smart contracts?

Accepted Answer

To log information to the blockchain that off-chain applications can listen to and act upon

Answer

To trigger external API calls from within the blockchain

Answer

To schedule timed future executions of contract functions

Answer

To enable direct communication and data sharing between two smart contracts

Question 6

What is the ERC-721 standard primarily designed for?

Accepted Answer

Creating non-fungible tokens (NFTs) where each token has a unique identity

Answer

Creating fungible tokens with a fixed maximum supply cap

Answer

Enabling a single contract to manage multiple different token types simultaneously

Answer

Defining how decentralized exchanges should route token swap orders

Question 7

What happens when a smart contract transaction runs out of gas during execution?

Accepted Answer

The transaction reverts, all state changes are rolled back, and the gas consumed is not refunded

Answer

The transaction partially completes and saves whatever state changes occurred

Answer

The Ethereum network automatically supplements the needed gas from a reserve pool

Answer

The smart contract is permanently disabled and removed from the blockchain