Which scientist thought that the atom was the smallest particle in the universe?
a. niels bohr
b. john dalton
c. j. j. thomson
d. ernest rutherford

The scientist thought that the atom was the smallest particle in the universe is John Dalton. The answer is letter B. He established the atomic theory which consists of five; elements are made of extremely small particles called atoms, atoms of different element have different sizes, mass and physic – chemical properties, atoms cannot be divided further, destroyed or created, atoms can combine to form compounds and in chemical reaction, atoms can be combined, separated or rearranged. J.J. Thompson discovered the electrons in the atom. Ernest Rutherford discovered the half – life of an atom and Neils Bohr explain the quantum mechanics.