How do you calculate the percent by mass of an element in a compound?

The characteristic of two different types of reactions are shown below. reaction a: electrons are gained by the atoms of an element. reaction b: protons are lost by the atom of and element. which statement is true about the atoms of the elements that participate in the two reactions? a: their identity changes in both reaction a and b. b: their identity changes in reaction a but not b. c: their identity changes in reaction b but not a. d: their identity remains the same.

Ineed to find the answer of this question because i dont understand it

Explain what happens at the saturation point when adding salt to water at room temperature.