Who first used the word "atomos" to describe the smallest unit of a substance? thomson democritus bohr schrödinger?

The correct answer is Democritus.

Explanation:

Democritus was a Greek philosopher and is still remembered for his contribution towards the atomic structure of the universe. He first described the smallest unit of a substance and named it as "atomos".

Thomson gave plum pudding model describing that electrons are surrounded by a soup of positive charge and to balance this positive charge,  negatively charged electrons are present, as there are plums in pudding.

Bohr gave the planetary motion of an atom where electrons are the planets that revolve around the nucleus considered as Sun.

Schrodinger gave the quantum mechanical model of an atom.

Hence, the correct answer is Democritus.

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.  

it is the most commonly accepted one