How much energy is equal to 1 kg of mass?

This implies, for instance, that 1 kilogram of matter is equivalent to an energy E = (1 kg)×(3×108 m/sec)2 = 9×1016 kg m2/sec2. An energy of 1 kg m2/sec2 is known as 1 joule, for short.

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.