Question

which is the atom having smallest size and why

Answer 1

The smallest is the hydrogen atom with one proton and one electron. Since electrons are about 2000 times less massive than protons (and neutrons), then the mass of an atom is mostly from the protons and neutrons. Atomic size is the distance between outermost shell and nucleus of an atom.
hope it helps u.....

Answer 2

Heya friend here is your ans
Hydrogen because it have one proton and one electron
Hope it helped you
Please mark me as brainlist
Please follow me