(sc.8.p.8.7) in the current model of the atom?

answer i need it

The answer for #3 is c but i don't know why

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

A4.86 g piece of metal was placed in a graduated cylinder containing 15.5 ml of water. the water level rose to 17.3 ml. what is the density of the metal. i need the steps of how to solve it to so i can use a formula to work out other problems.