If the shortest wavelength of the $He^{+}$ ion in the Balmer series is $X \ m$,then the longest wavelength in the Paschen series of the $Li^{2+}$ ion is:

Values of work function $(W_0)$ for a few metals are given below:

Metal	$Li$	$Na$	$K$	$Mg$	$Cu$	$Ag$
$W_0 / eV$	$2.42$	$2.3$	$2.25$	$3.7$	$4.8$	$4.3$

The number of metals which will show photoelectric effect when light of wavelength $400 \ nm$ falls on it is $........$.
Given: $h = 6.6 \times 10^{-34} \ J \ s$,$c = 3 \times 10^8 \ m \ s^{-1}$,$e = 1.6 \times 10^{-19} \ C$

Calculate the radius of the first orbit of $Be^{3+}$. (in $pm$)

As we move away from the nucleus,the energy of the electron

What is the radius of the fourth orbit of $Be^{3+}$ (in $pm$)?

The total energy of the electron in the hydrogen atom in the ground state is $-13.6 \, eV$. What is the stopping potential in volts required to remove this electron from the ground state?