The mass number of an atom is equal to which of the following? question 15 options: the number of protons in a nucleus the number of protons plus the number of electrons in an atom the number of electrons circling the nucleus of an atom the number of protons plus the number of neutrons in a nucleus

Mass number is equal to the number of protons plus the number of neutrons in a nucleus of an atom

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).