The radius of the first Bohr orbit of a hydrogen atom is $0.53 \times 10^{-8} \ cm$. The velocity of the electron in the first Bohr orbit is

Which of the following statements is $NOT$ correct regarding the Bohr model?

If the radius of the hydrogen atom is $53 \, pm$, the radius of the $He^{+}$ ion is closest to $...... \, pm$.

Angular momentum of an electron in the $n^{th}$ orbit of a hydrogen atom is given by

Which of the following statements are correct?
$I$) The energy of hydrogen atom in its ground state is $-13.6 \ eV$
$II$) On the basis of Bohr's model,the radius of the $3^{rd}$ orbit of hydrogen atom is $158.7 \ pm$
$III$) The order of radius of the first orbit of $H, He^{+}, Li^{2+}$ and $Be^{3+}$ is $H > He^{+} > Li^{2+} > Be^{3+}$

First and second excitation potentials of hydrogen atom (in $eV$) would be respectively