Answer:
2. When the ideas in both clauses are closely related
Step-by-step explanation:
One of the uses of semicolons is to link two independent clauses whose ideas are closely related and are not linked with a conjunction like "and". By putting semicolons in this situation, we also convey that those are ideas are equally important.
The other options are incorrect because the semicolon is not used to link independent clauses with phrases nor dependent clauses because neither of these units expresses a complete thought or idea. (Options 1 and 3). Option 4 is also wrong because in order to separate simple items in a series, a comma, and not a semicolon, is used.