The radius of the innermost electron orbit of a hydrogen atom is $5.3 × 10^{-11}m$. The radius of the third orbit is:

$4.77 × 10^{-10} m$

The correct answer is Option (1) → $4.77 × 10^{-10} m$

$r_n$, Radius of an electron orbit, in hydrogen orbit in a hydrogen atom is -

$r_n=n^2r_0$

where,

n = principle quantum number of the orbit = 3

$r_0$ = Radius of 1st orbit = $5.3×10^{-11}m$

$∴r_3=(3)^2×5.3×10^{-11}$

$=4.77×10^{-10}$