Sam believes the rock is more dense than the pencil. He measured the mass of the rock to be 8.5 grams and volume to be 4.5mL. He measured the mass of the pencil to be 2.4 grams and volume to be 4.5mL. Density is the mass per unit volume of an object. When he put the rock and pencil into the water, the pencil floated and the rock sank. Which is more dense? Give your reasoning using actual density values.

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.  

the answers would be

the first one and the second one