The percent of a solute in a solution is defined as the mas of solute in 100 grams of solution. A 20% solution of sulfuric acid contains 20% pure H2SO4 by mass and 80% pure H2O by mass. In 100 grams of H2SO4 there are 20 grams of sulfuric acid and 80 grams of water. Assume water is the solvent. If 18.0 grams of sodium sulfate are dissolved in 207.0 grams of water, what is the percent concentration of this solution?

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.