Final answer:
The statement that is not true is c) Electrons have a mass of 1 atomic mass unit. Electrons are much lighter than protons and neutrons, which have masses close to 1 amu. Electrons have a mass of only 0.00055 amu.
Step-by-step explanation:
The statement that is not true among the given options is c) Electrons have a mass of 1 atomic mass unit (amu). Protons and neutrons have a mass that is approximately equal to 1 amu, with protons at about 1.0073 amu and neutrons at around 1.0087 amu. On the other hand, electrons are much lighter with a mass of only 0.00055 amu. Therefore, electrons do not have a mass of 1 amu.
The atomic number is indeed equal to the number of protons in an atom, making the statement d) true. The positive charge on a proton is equal in magnitude to the negative charge on an electron, and given that a neutral atom has an equal number of protons and electrons, this makes statements a) and b) true as well.