Which of the following types of classified materials require standard classification markings?

Instant messages require standard classification markings because they often contain sensitive information that could affect national security if improperly disclosed. As classified communication channels, instant messages can serve as a medium for sharing controlled unclassified information or classified data, thus necessitating adherence to proper classification protocols.

Standard classification markings serve to indicate the level of classification and handling requirements for the information contained within the message. This helps ensure that individuals handling the information recognize its sensitivity and take appropriate measures to protect it. Messages that lack these markings could lead to the inadvertent sharing of protected information, which is why it is crucial to apply standard classification markings to instant messages containing classified content.

In contrast, text messages, social media posts, and public announcements generally fall outside of classified communication protocols. While they can also contain sensitive information, they are not typically classified in the same structured manner and often do not require these standard markings. Thus, the correct choice focuses on the need for appropriate handling of instant messages under classification guidelines.