Which of the following is an example of a smart contract?

A smart contract is best defined as a digital agreement that is executed on the blockchain. This type of contract leverages the decentralized and immutable nature of blockchain technology to facilitate, verify, and enforce the terms of an agreement automatically without the need for intermediaries. Smart contracts are coded as software that runs on the blockchain, enabling them to be self-executing when predefined conditions are met.

In contrast, physical contracts, standard commercial contracts, and centralized agreements do not utilize blockchain technology. Physical contracts are tangible documents, while standard commercial contracts might be written in legal terms but lack the automation and enforcement aspects inherent in smart contracts. Centralized agreements are managed by a single party, which runs counter to the decentralized model that smart contracts exemplify. The key aspect lies in the on-chain execution and automated nature that characterizes smart contracts, making the digital agreement executed on the blockchain the correct choice.