Which of the following is the best example of a mand?

A mand is a type of verbal operant that involves a request for something specific, often motivated by a particular need or desire. In this context, the statement "More juice!" clearly demonstrates this concept because the child is expressing a specific desire to have more juice due to their thirst. This utterance is a direct request for an item that fulfills a need, which is the essence of what a mand is.

The other options do not fit the definition of a mand as effectively. Pointing to a toy expresses interest or a desire for attention, but it is not a verbal request. A parent instructing a child to clean up doesn't represent a request from the child but rather a directive imposed by an adult. Inquiring "What is that?" suggests a request for information rather than a request for an object or action that the speaker wants, placing it outside the category of a mand. Therefore, the child asking for "more juice" is the clearest example of a mand.