$A$ certain transition in the hydrogen spectrum from an excited state in one or more steps gives rise to a total of $10$ lines. The number of lines lying in the visible spectrum is:

In which hydrogen-like ion is the difference in wavelength between the first line of the Balmer series and the first line of the Lyman series equal to $59.3 \ nm$? $[R_H = 109678 \ cm^{-1}]$

The work functions (in $eV$) of $Mg, Cu, Ag, Na$ respectively are $3.7, 4.8, 4.3, 2.3$. From how many metals,the electrons will be ejected if their surfaces are irradiated with an electromagnetic radiation of wavelength $300 \ nm$ ?
$(h=6.6 \times 10^{-34} \ Js, 1 \ eV=1.6 \times 10^{-19} \ J)$

The radii of two of the first four Bohr’s orbits of the hydrogen atom are in the ratio $1 : 4$. The energy difference between them may be

The wavelength of the first line of the Lyman series for hydrogen is $1216 \ \mathring{A}$. The wavelength of the first line of the same series for a $10$ times ionized sodium atom $(Z = 11)$ will be ......... $\mathring{A}$.

In an orbital,the value of $K.E.$ is equal to: