which of the following are binary?

Depends on how you are using the term "binary".

I spent 35 years as a computer programmmer so I usually think of binary in a mathematical sense.

But in chemistry you could mean:

1. Compounds composed of only two atoms.

That would include Cl2, CaO, and HBr only.

or you could mean

2. A Compound composed of two different types of atoms:

That would inlcude CaO, HBr, CuCl2, AsH3, and NO2.

But my guess is that the teacher wants the first definition.

By the way, Cl2 is usually not called a binary molecule but rather a "diatomic molecule". There is nothing very important about the word "binary" in chemistry.

Cl2, CaO, HBr.