Bohr’s radius for the H-atom (n = 1) is approximately 0.53 Å. The radius of the first excited state (n = 2) orbit is;

The Bohr model gives the radius of an electron orbit in a hydrogen‑like atom as

$r=a{0}_0{n}^2$

where

$a{0}_0$ is the Bohr radius for the ground state (n = 1) and $n$ is the principal quantum number.

From the problem statement the ground‑state Bohr radius is

$a_0=0.53 \AA$

We need the radius for the first excited state, which corresponds to $n=2$. Plugging the values into the formula:

$r$₂=0.53 Å×22

Since $2^2$ = 4, we have

$r$₂=0.53 Å×4

Carrying out the multiplication:

$r$₂=2.12 Å

Thus, the radius of the n = 2 orbit is 2.12 Å, which matches the provided correct option.