The mass number of an element is equal to
a. the total number of electrons in the nucleus
b. the total number of protons and neutrons in the nucleus
c. less than twice the atomic number
d. a constant number for the lighter elements

b. the total number of protons and neutrons in the nucleus

Explanation:

Mass number is defined as the sum of number of protons and neutrons that are present in an atom.

Mass number = Number of protons + Number of neutrons

In an atom, when neutrons or protons are lost or gains, it directly affects the mass number of an atom.

Atomic number is defined as the number of protons or number of electrons that are present in an atom.

Atomic number = Number of electrons = Number of protons

Thus the mass number of an element is equal to the total number of protons and neutrons in the nucleus.

a. a primary source combines several different accounts of an event. b. a primary source generally benefits from having been written after an event.

explanation: