In terms of Bohr radius a_o the radius of 2nd Bohr orbit of Hydrogen…

The correct answer is Option (1) → \( 4 a_o \)

In Bohr's model the radius of the \( n \)th orbit of hydrogen grows as the square of \( n \):

    \( \displaystyle r_n = n^{2}\,a_o \)

For the second orbit, \( n = 2 \):

    \( \displaystyle r_2 = 2^{2}\,a_o = 4\,a_o \)

NCERT (2026-27):
Bohr Model of the Hydrogen Atom – “… For a hydrogen atom, Eq. (12.4) gives the expression to determine the energies of different energy states. But then this equation requires the radius r of the electron orbit. To calculate r, Bohr’s second postulate about the angular momentum of the electron—the quantisation condition—is used. The radius of n^th possible orbit thus found is

    \( \displaystyle r_n = \left(\frac{n^{2}}{m}\right)\left(\frac{h}{2\pi}\right)^{2}\frac{4\pi\varepsilon_0}{e^{2}} \qquad (12.7) \) ”