Question

What element has a mass number of 65?

Answer 1

zinc

Explanation:

Zinc, which has 30 protons, has a mass number of 65.39 amu.

This means zinc has 30 protons and around 35 to 36 neutrons, depending on various isotopes that may form.

Answer 2

Copper has an isotope with a mass number of 65, which is called copper-65.

Explanation:

Isotopes of an element have the same atomic number (number of protons), but different numbers of neutrons. An isotope is named for its mass number.

Copper has two stable isotopes found in nature, copper-63 and copper-65. Copper is the only element that has a stable isotope with a mass number of 65.

http://www.periodictable.com/Properties/A/StableIsotopes.html
https://en.wikipedia.org/wiki/Copper