Acovalent chemical bond is one in which a. outer-shell electrons of two atoms are shared so as to satisfactorily fill their respective orbitals b. outer-shell electrons of one atom are transferred to fill the inner electron shell of another atom c. electrons are removed from one atom and transferred to another atom so that the two atoms become oppositely charged d. protons and neutrons are shared by two atoms so as to satisfy the requirements of both atoms e. electrons from the same atom, but opposite spins, are paired

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.