Step-by-step explanation:
According to Bohr's model, angular momentum is given by :

Since, L = m v r
So,

...................(1)
The electrostatic force is balanced by the electrostatic force as :

From equation (1),

Where
r is the radius of ground state hydrogen atom
n is the orbit
h is Planck's constant
m is the mass of electron
k is the electrostatic constant


Diameter of hydrogen atom,


So, the diameter of a ground-state hydrogen atom is
. Hence, this is the required solution.