Be more specific, I could possibly find the asnwer you're looking towards.
(g solute/g solution)*100 = % mass/mass
30 g / 400 * 100
0,075 * 100
= 7,5% w/w
hope this helps!
Answer: It depends on the element.
Explanation: Every element has a different amount of protons in its nucleus. It is the same as its atomic number on the periodic table. For example: Hydrogen has an atomic number of 1 because it has 1 proton in its nucleus, Helium has 2, Carbon has 6, Platnium has 78, and so on...