Which may change when the manipulated variable changes? independent variable controlled variable responding variable operational variable

The independent variable, also known as the manipulated variable, is what you change to check out the responding (or dependent) variable to see how the changing your manipulated variable affects the responding variable. The controlled variable should stay the same at all times, as that could mess up the calculations (for example, if you're going to see how hungry the average person is, you don't want to ask someone before eating while another right after eating). There's no such thing as the operational variable, so we're left with A and B. Since the question asks 'may change' and not 'will change', it's not A due to that it will change no matter what with that. However, for B, the controlled variable (what you're testing, for example, the effect of how hungry you are based on what time it is. In this, you're changing the time (independent variable) while you want to see if there is a difference on how hungry people are (the responding variable) so you're not 100% sure how the hunger of people changes but you're sure that you're changing the time when you change the time) may or may not change so it's correct

Outermost (valence) electrons

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom.