What does a node in the blockchain network do?

In a blockchain network, a node plays a critical role in maintaining the integrity and functionality of the system. Specifically, its primary duty is to process and validate transactions that occur on the network. Nodes receive transaction data, verify it against the existing blockchain's rules and protocols, and then participate in reaching consensus with other nodes to confirm the validity of those transactions.

Once a transaction is validated, it is grouped into a block, which is then added to the blockchain after agreement is achieved amongst the participating nodes. This decentralized validation process enhances security and trust, making it difficult for fraudulent activities to take place, as altering any transaction would require the consensus of the network's nodes.

The other options do not accurately describe the primary function of a node within a blockchain network. While user interfaces for cryptocurrency exchanges, creation of new cryptocurrencies, and user account management are important aspects of the broader blockchain ecosystem, they do not pertain to the essential processing and validation tasks that a node is designed to perform.