Final answer:
Phosphorus, with an atomic number of 15, always has 15 protons in its nucleus and 15 electrons in a neutral state.
Step-by-step explanation:
From its atomic number of 15, it is possible to predict that phosphorus always has 15 protons. The atomic number of an element is defined as the number of protons in the nucleus of an atom of that element. In all electrically neutral atoms, the number of prostons is equal to the number of electrons. So, phosphorus also has 15 electrons when it is neutral. The number of neutrons can vary among different isotopes of phosphorus, so the atomic number does not provide information about the neutron count. Hence, option "e" stating phosphorus has 15 protons is correct.