What are the main functions of the human skeletal system? A To support the body, protect the organs, produce blood cells, and store calcium.
To regulate the composition of body fluids by removing metabolic wastes and retaining a balance of water, salt, and other
nutrients
OcTo regulate and maintain bodily functions by producing hormones and releasing them into the bloodstream.
D. To enable the diffusion of oxygen into the bloodstream and the removal of carbon dioxide from the bloodstream.

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.  

wher is the rest of the question