Question

What nuclear symbol has 13 protons and 15 neutrons

Answer 1

It's an isotope of Aluminum so you would write "Al" with a "28" in the top left corner

Answer 2

It's simple.
The number of protons in an atom never changes. And also, the no of protons is its atomic number. If you look up the periodic table, you will find a number on the top - left corner of each of the boxes. This is the atomic number. No 2 same elements on the periodic table have the same atomic number. So, all you have to do is search for a box that has the number 13 on it.

and by the way ... the element which you're searching for is Aluminium.