The diameter of an atom is in the order of________________?

C. 0.2nm

The diameter of an atom is in the order of 0.2 nm (nanometers), which is equivalent to 0.0000002 mm. Atoms are extremely small and cannot be seen with the naked eye. In fact, they are so small that they are measured in nanometers or picometers (1 nm = 10^-9 m, 1 pm = 10^-12 m). The size of an atom is determined by the size of its nucleus, which is much smaller than the electron cloud surrounding it. The electron cloud is what gives an atom its overall size and determines how it interacts with other atoms and molecules.