If a potassium atom loses one electron than it becomes a +1 charge, because the electrons are negative and the nucleus is positive (the positive comes from the protons). The protons and electrons balance out so it has a neutral charge, but if the atom loses an electrons it has a positive charge, but if the atom gains an electron than it becomes negative. the charge (+/- and the number) of the atom depends on how many electron the atom gains/loses.
the answer is (D.) +1
I hope this helps.
