Answer:
The word that should be placed in place of __ is "tone".
Step-by-step explanation:
A formal tone is a type of language structure that you should use in professional, academic, and literary circles. However, it is not limited to these uses and can be part of your routine also when you communicate by email or start a conversation with someone with whom you do not have much intimacy. In short, formal tone should be used in any kind of formal writing. For this reason, we can conclude that in any kind of formal writing, the writer must use a formal tone or attitude towards the subject.