Which best explains the difference between a ball-and-stick model of a chemical compound and a space-filling model?
Ball-and-stick models can show compounds in three dimensions, but space-filling models cannot.
Space-filing models can show compounds in three dimensions, but ball-and-stick models cannot.
Ball-and-stick models show the bonds between atoms, but not the relative sizes of atoms. Space-filling models show the relative sizes of atoms, but not the bonds between atoms.
Space-filling models show the bonds between atoms, but not the relative sizes of atoms. Ball-and-stick models show the relative sizes of atoms, but not the bonds between atoms.

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.

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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.  

confused

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the answer is 0.42 is that is an option. this question provides no info