Question

Which of the following is unique for any given element?

Answer 1

Atomic number is the unique property for each element 

Answer 2

The answer is could either be protons or the atomic number. I would go with the atomic number.

The number of protons equals the atomic number on the periodic table. Every atom of a particular element contains the same number of protons. Each element has a unique atomic number, or a unique number of protons in its nucleus.

I hope this helped.