No, there is no known atom that is the size of a mountain. Atoms are incredibly tiny particles, with sizes on the scale of picometers (trillionths of a meter). The size of an atom is determined by the arrangement and distribution of its electrons around the nucleus.
To give you a sense of scale, a typical atom, such as a hydrogen atom, has a radius of about 0.1 nanometers (1 nanometer = 1 billionth of a meter). Even larger atoms like uranium have radii on the order of a few picometers.
In contrast, mountains are massive geological formations that can span kilometers in length and height. They are composed of various minerals and rocks, which are made up of countless atoms bound together.
Therefore, the size difference between an atom and a mountain is enormous. Atoms are on the scale of angstroms and picometers, while mountains are on the scale of kilometers.