The atomic number tells you the number of in one atom of an element. It also tells you the number of in a neutral atom of that element. The atomic number gives the “identity “of an element as well as its location on the Periodic Table. No two different elements will have the atomic number.

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.  

plasma - state of matter made up of electrically charged particles