This question is asking what happens to atomic mass and atomic number during electron capture. The question stem defines electron capture as a type of nuclear reaction in which an electron is added to the nucleus, causing a proton to turn into a neutron. The atomic number represents the number of protons, while the atomic mass includes both protons and neutrons. Electrons are essentially massless and would not contribute to the atomic mass. Predict that with one less proton, the atomic number will decrease, but since the total number of neutrons and protons remains the same, the atomic mass will remain the same.