In the electron cloud model, electrons are said to be moving so fast that a person can

Not determine their exact position.

Explanation:  In the electron cloud model, electrons are said to be moving so fast that a person cannot determine their exact position.

This phenomenon goes well off with the Heisnberg Uncertainity Principle (HUP)which states that the momentum (Δm) and position (Δx) of an obejct cannot be determined simultaneously at the same time.

The mathematical relation of HUP is -

                                      Δx Δm ≥ h/ 4π

where h = Planck's Constant

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.  

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.