$1$ mole of photons, each of frequency $2500 \ s^{-1}$, would have approximately a total energy of:

Assertion : Angular momentum of an electron in any orbit is given by angular momentum $= \frac{nh}{2\pi}$,where $n$ is the principal quantum number.
Reason : The principal quantum number,$n$,can have any integral value.

The figure shows six spectral lines in an emission spectrum arising from energy level transitions. Which of the following spectral lines does not appear in the absorption spectrum?

Ejection of the photoelectron from metal in the photoelectric effect experiment can be stopped by applying $0.5\, V$ when the radiation of $250\, nm$ is used. The work function of the metal is ................ $eV$

Which of the following statements are correct,if the threshold frequency of caesium is $5.16 \times 10^{14} \ Hz$?
$A.$ When $Cs$ is placed inside a vacuum chamber with an ammeter connected to it and yellow light is focused on $Cs$,the ammeter shows the presence of current.
$B.$ When the brightness of the yellow light is dimmed,the value of the current in the ammeter is reduced.
$C.$ When a red light is used instead of the yellow light,the current produced is higher with respect to the yellow light.
$D.$ When a blue light is used,the ammeter shows the formation of current.
$E.$ When a white light is used,the ammeter shows the formation of current.
Choose the correct answer from the options given below:

The energy of an electron in the first Bohr orbit of the $H$ atom is $-13.6 \, eV$. The energy value of an electron in the first excited state of the $H$ atom is ............ $eV$.