If the ionisation potential of a helium atom is $24.6 \, V$,the energy required to ionise it will be

If elements with principal quantum number $n > 4$ were not allowed in nature,then the number of possible elements would be

The spin quantum numbers $+1/2$ and $-1/2$ indicate that...

$A$ beam of ultraviolet light of all wavelengths passes through hydrogen gas at room temperature,in the $x-$ direction. Assume that all photons emitted due to electron transition inside the gas emerge in the $y-$ direction. Let $A$ and $B$ denote the lights emerging from the gas in the $x$ and $y$ directions respectively.

Which of the following spectra contains all frequencies from the high to the low frequency range?

Continuous spectrum is not produced by which of the following?