g A chemical equilibrium exists when: A chemical equilibrium exists when: there are equal amounts of reactants and products. the rate at which reactants form products is the same as the rate at which products form reactants. the sum of reactant and product concentrations equals one mole. reactants are completely changed to products. the rate at which reactants form products becomes zero.

explanation:

detials on each model with digrams

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.  

i do not get it   at all