Final answer:
An element with an atomic number of 17 has 17 protons in its nucleus, which corresponds to the element chlorine. This atomic number defines the element's identity and is conserved in nuclear reactions.
Step-by-step explanation:
If the atomic number is 17, then the number of protons in the nucleus of an atom of that element is also 17. In nuclear reactions, the conservation of protons and neutrons is a fundamental principle.
For example, if we consider a nuclear reaction with an unknown product that has a mass number of A = 35 and an initial atomic number of Z = 16, adding a particle with a charge of -1 would give the product an atomic number Z = 17.
The element with an atomic number 17 is chlorine, which would be reflected in a balanced nuclear equation showing the conversion of other elements or isotopes to chlorine.