Blockchain Developer FREE Blockchain Developer Token Standards and NFTs Questions and Answers 2

Question 1

Which ERC standard introduced the concept of semi-fungible tokens by combining fungible and non-fungible token functionality in a single contract?

Accepted Answer

ERC-1155

Answer

ERC-1155 is a multi-token standard that supports both fungible and non-fungible tokens within one contract, making them semi-fungible.

Question 2

What function in the ERC-721 standard is used to safely transfer an NFT while ensuring the recipient contract can handle it?

Accepted Answer

safeTransferFrom

Answer

safeTransferFrom checks whether the recipient implements the ERC721Receiver interface, preventing tokens from being locked in incompatible contracts.

Question 3

In ERC-20, what happens if a user calls transfer() with an amount exceeding their balance?

Accepted Answer

The transaction reverts

Answer

The ERC-20 transfer function will revert the entire transaction if the sender's balance is insufficient.

Question 4

What is the primary purpose of the tokenURI function in ERC-721?

Accepted Answer

To return a URI pointing to the token's metadata

Answer

The tokenURI function returns a URI that points to a JSON file containing the NFT's metadata such as name, description, and image.

Question 5

Which vulnerability can occur when an ERC-20 token's approve function is called to change an existing allowance without first setting it to zero?

Accepted Answer

Front-running double-spend attack

Answer

A spender can front-run the approve transaction to spend both the old and new allowance, resulting in a double-spend.

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