Atoms of the main group elements either gain or lose electrons so they have eight electrons in the outermost energy level. In doing so, they attain a noble gas electron configuration. Match these elements with the number of electrons they gain or
lose. Consult the periodic table to help answer the question.
Drag each tile to the correct box.
Ma

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.  

i think it's letter a.