According to Bohr's theory,the angular momentum of an electron revolving in the second orbit of a hydrogen atom will be:

When a hydrogen atom is in its first excited level,its radius is .... of the Bohr radius.

The radius of the innermost electron orbit of a hydrogen atom is $5.3 \times 10^{-11} \text{ m}$. What is the radius of the $n = 3$ orbit?

The de-Broglie wavelength of the electron in the ground state of a hydrogen atom is ........ $\mathring{A}$.

$A$ beam of monochromatic light is used to excite the electron in $Li^{++}$ from the first orbit to the third orbit. The wavelength of monochromatic light is found to be $x \times 10^{-10} \; m$. The value of $x$ is $\dots$. [Given $hc = 1242 \; eV \cdot nm$]

Neglecting the reduced mass effect,which optical transition in the $He^+$ spectrum has the same wavelength as the first Lyman transition of hydrogen ($n = 2$ to $n = 1$)?