Explanation:

Here’s the thing—let’s break this down:

- The sentence says: “The radio comes (1)______ automatically at 7 o’clock…”

- You need a preposition that works with “comes… automatically.”

- "in" (Option 1): “Comes in automatically” is off. We don’t say that about devices turning on.

- "of" (Option 2): “Comes of automatically” doesn’t make sense at all.

- "on" (Option 3): This fits how we talk. “The radio comes on automatically”—that’s exactly how we describe something starting by itself.

- "off" (Option 4): This is the opposite of what you need. “Comes off” means it stops, not starts.

So, Option 3—on—is correct. You picked exactly the right answer.