Choose the correct definition of an atom's atomic number. choose the correct definition of an atom's atomic number. an atom's atomic number is the number of protons it has in its nucleus. an atom's atomic number is the number of particles it has in its nucleus. an atom's atomic number is the number of electrons it has in its nucleus. an atom's atomic number is the number of neutrons it has in its nucleus.

the volume increases

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.