7) determine the number of tin atoms in 7.5 moles of tin.
the molar mass of tin is 118.71 g/mol

4.5 x 10^24 atoms of tin

Explanation:

We do not need to use the molar mass because we only need to know that 1 mol of something = 6.022 x 10^23 atoms of that thing.

7.5 mol tin x (6.022 x 10^23 atoms/1 mol tin)

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.