As heat is added to a substance undergoing a phase change, the temperature remains constant because the energy is being used to break covalent bonds lower the specific heat capacity overcome intermolecular forces oppose electron cloud repulsions

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.  

because of all the things that happen around the us, many people get into arguments which sadly could get physical, but we should actually make a change for that.