Blockchain Developer Token Standards and Creation 2

Question 1

Which ERC-20 function returns the number of tokens a spender is still allowed to withdraw from an owner's account?

Accepted Answer

allowance(owner, spender)

Answer

balanceOf(owner)

Answer

approve(spender, amount)

Answer

transferFrom(from, to, amount)

Question 2

In ERC-20, what is the well-known race-condition risk associated with the approve() function?

Accepted Answer

A spender can front-run a changed approval and spend both the old and new amounts

Answer

It permanently locks the owner's balance

Answer

It mints unlimited tokens

Answer

It bypasses the totalSupply cap

Question 3

What does the ERC-20 decimals() function actually control?

Accepted Answer

Only the display formatting of token amounts off-chain

Answer

The on-chain divisibility enforced by the contract

Answer

The maximum total supply

Answer

The gas cost of transfers

Question 4

Which event must an ERC-20 token emit when tokens move between addresses?

Accepted Answer

Transfer(from, to, value)

Answer

Approval(owner, spender, value)

Answer

Sent(operator, from, to)

Answer

Mint(to, value)

Question 5

Why is it best practice to emit a Transfer event from the zero address when minting ERC-20 tokens?

Accepted Answer

So off-chain indexers can track supply changes consistently

Answer

Because the EVM rejects mints without it

Answer

To reduce gas costs

Answer

To prevent reentrancy

Question 6

What problem does the ERC-2612 'permit' extension solve for ERC-20 tokens?

Accepted Answer

It allows gasless approvals via off-chain signed messages

Answer

It increases the maximum supply

Answer

It adds NFT metadata

Answer

It enables cross-chain bridging automatically

Question 7

If an ERC-20 transfer() returns false instead of reverting, what is the recommended way to handle it safely in a calling contract?

Accepted Answer

Use a SafeERC20 wrapper that checks the return value and reverts on failure

Answer

Ignore the return value since transfers always succeed

Answer

Retry the transfer in a loop

Answer

Call selfdestruct on failure