First, please use code-tags when posting code and not plain-text.
Second, this isn’t a Unity thing, it’s a simple C# thing and if I’m honest, just lack of attention or maybe understanding of what types are.
You defined a field of type “Rigidbody” named “rb” then go and try to assign a completely different type to it i.e. a “Rigidbody2D”. Look at the error again, this is what it’s telling you.