Answer correctly and dont bother coming to this question if you have the wrong answer.

it's b or d I am not 100% sure witch one tho

B.

Explanation:

It is B because it says which is an example of A PHYSICAL MODEL. B is a physical model becuase by using tennis balls to represent the plantes (including the sun)

it is a model of a problem!!!

Have a great day!

Hope this helps!

-Lea

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.