An ion that consists of 7 protons, 9 neutrons, and 10 electrons has a net charge of A) 2–
B) 2+
C) 3+
D) 3–
The answer is D. Why the answer is not A but D? Can you explain?

According to the passage, which of these is true about gray water systems? a) gray water systems use plants that require less water. eliminate b) gray water systems require the use of less fossil fuels. c) gray water systems reduce the amount of fresh water used. d) gray water systems reduce the amount water used by shower heads.