When an electron jumps from the $n = 4$ level to the $n = 1$ level,the angular momentum of the electron changes by:

The orbital magnetic moment $(m_{orb})$ of a revolving electron around the nucleus varies with the principal quantum number $(n)$ as

The radius of the orbit of an electron in a $H$-atom changes from $2.12 \mathring{A}$ to $4.77 \mathring{A}$. The $H$-atom has:

The de-Broglie wavelength of an electron in the ground state of the hydrogen atom is

$A$ 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 $hc = 1242 \; eV \cdot nm$]

In Bohr's theory of the hydrogen atom,'$r$' is the radius of the orbit,'$V$' is the speed of the electron, and '$E$' is the total energy of the electron. Which of the following physical quantities is inversely proportional to the principal quantum number '$n$'?