When 5 grams of salt dissolve in 30 grams of water, what is the resulting mass of the mixture?

The answer is 35 grams.

When we mix salt and water, salt will dissolve. Still, it mass does not disappear, but remains intact. Mass cannot be destroyed. When salt is dissolved in the water, salt molecules are only re-positioned, but all the molecules are present as well as their mass. So if you add 5 grams of salt in 30 grams of water, the resulting mass will be 5 + 30 grams, which is 35 grams.