What protocol is commonly used for secure data transmission on the internet?

The correct choice for secure data transmission on the internet is HTTPS. This protocol stands for Hypertext Transfer Protocol Secure and is essentially an extension of HTTP. The key feature of HTTPS is that it encrypts the data being transmitted between the user's browser and the web server, which helps secure sensitive information from eavesdropping and tampering.

HTTPS employs SSL/TLS (Secure Sockets Layer / Transport Layer Security) to create a secure channel over an insecure network. This means that any data exchanged, such as passwords, credit card numbers, and personal information, is encoded in such a way that only the intended recipient can decrypt and read it. This makes HTTPS particularly critical for online transactions, login pages, and any exchanges where privacy and security are imperative.

In contrast, the other choices serve different purposes: HTTP is the standard protocol for unencrypted web traffic, FTP is used for transferring files between systems but does not inherently encrypt data, and SMTP is a protocol for sending emails that also does not focus on encryption. Thus, HTTPS stands out as the primary protocol for secure data transmission on the internet.