The correct answer is B. Protons and electrons have the same mass.
Explanation:
An atom, which is the unit of mass, is composed of protons and neutrons that are in the nucleus, along with electrons that orbit the nucleus. In terms of mass, protons that are particles positively charged and neutrons that do not have a charge have the same mass that is around 1.67 x Kg or 1 AMU (Atomic mass unit). However, in the case of electrons, these have less mass than protons or neutrons and the difference of mass is important as electrons have a mass of only 9.10 x Kg or 0 AMU. Thus, the statement that is incorrect about atomic structure is "Protons and electrons have the same mass" because protons are much more massive than electrons.