Final answer:
The mass number of the element is 14.
Step-by-step explanation:
The mass number of an atom is the sum of its protons and neutrons. An element with 7 protons, 7 neutrons, and 10 electrons has a mass number that is the sum of the protons and neutrons.
The mass number of an element is equal to the number of protons plus the number of neutrons. In this case, the element has 7 protons and 7 neutrons, so the mass number would be:
Mass number = number of protons + number of neutrons
Mass number = 7 + 7
Mass number = 14