Which of the following properties of an unknown substance would allow it to be classified as a mixture? The unknown substance –has an overall density greater than that of water. is able to easily conduct an electric current. is composed throughout of the same two elements. has different properties when sampled in different areas.

the answer is a and have a great day

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.