A certain isotope x2 + contains 48 electrons and 75 neutrons. what is the mass number for this element?

The most important identity of an element is its atomic number or number of protons. Electrons and neutrons may vary, but protons stay constant. To start with, when an element is neutral, the number of protons and electrons are equal. When the isotope is a positive ion, that means that the element gives away 2 electrons. So, if the electrons is 48, then that means it was originally 48 - 2 = 46 electrons. From the periodic table, element 46 is Palladium (Pd).