* Mass Number: The mass number is the total number of protons and neutrons in an atom's nucleus.

* Protons: Sulfur always has 16 protons (this defines it as sulfur).

* Neutrons: You've given the number of neutrons as 17.

Calculation:

Mass number = Protons + Neutrons

Mass number = 16 + 17

Mass number = 33

Therefore, the mass number of this sulfur atom is 33.

Important Note: The number of electrons doesn't affect the mass number. Electrons are much less massive than protons and neutrons, so their contribution to the atom's overall mass is negligible.