How to make Object1 check if Object2 has been destroyed? (in c#)

I am working on a little game where in one Level there are multiple enemies with the Tag "Enemy" and I want the player to check if every enemy has been destroyed and if yes it should change to another Scene. (Btw. Im a totally beginner so pls don´t judge me and I need it in like 2 weeks because its a school project(not kidding)) Thanks