Chemistry is
a. a characteristic of a substance that can be observed without changing the substance into another substance.
b. the study of matter and how matter changes.
c. anything that has mass and takes space
d. a rapid reaction between oxygen and a substance called fuel.

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

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.