What is an example of a rule in the statement logic. Additionally, derive this rule.?

Answer 1

"Any atomic statement is a well-formed formula or a sentence."

This is a axiom or definition of a rule in statement logic.  Deriving it is an exercise in stating the obvious and/or the reflexive.

Basically, speaking or writing in complete sentences is the only valid logical form:  ~ subject-predicate-object.  An incomplete sentence is invalid.  Similar rationale for a wff.