Q 12-12-015NEETJEE MainMedium
The radius of the first Bohr orbit of hydrogen is $0.53$ Å. The radius of the second orbit of He$^+$ is
Answer: (D) $1.06$ Å
$r_n = 0.53\dfrac{n^2}{Z}$ Å $= 0.53 \times \dfrac{4}{2} = 1.06$ Å.
Solution by Sreeraj P, M.Sc Physics