When the primary function of communication is to convey new information, it is known as:

The correct option is Referential function.

In communication theory, particularly Roman Jakobson's model of the functions of language, communication is analyzed based on its primary focus or goal. When the main purpose of a message is to convey information, facts, ideas, or describe a situation/context, it performs the referential function (also sometimes called the informative or cognitive function).

Here is a breakdown of why this is correct and why other options do not apply:
1. Referential Function: This function is focused on the 'context' or the referent. It is used to describe a situation, object, or mental state, providing information that can be tested for truth or falsehood (e.g., "The water is boiling" or "The meeting starts at 3 PM"). Since conveying new information is the primary goal, this is the correct classification.
2. Subliminal function: This refers to communication that operates below the threshold of conscious awareness, which is not primarily about conveying explicit new information.
3. Single task function: This is not a standard category in established communication models.
4. Differential function: This term is not used to describe the informative aspect of primary communication functions.