In a $He-Ne$ laser,the metastable state exists in:

Match the appropriate pairs from List-$I$ and List-$II$:

List-$I$	List-$II$
$1$. Nitrogen molecules	$(A)$ Continuous spectrum
$2$. Incandescent solids	$(B)$ Absorption spectrum
$3$. Fraunhofer lines	$(C)$ Band spectrum
$4$. Electric arc between iron rods	$(D)$ Emission spectrum

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

Ionisation energy of $Li$ (Lithium) atom in ground state is $5.4 \ eV$. Binding energy of an electron in $Li^+$ ion in ground state is $75.6 \ eV$. Energy required to remove all three electrons of Lithium $(Li)$ atom is ........... $eV$.

Highly excited states for hydrogen-like atoms (also called Rydberg states) with nuclear charge $Ze$ are defined by their principal quantum number $n$,where $n \gg 1$. Which of the following statement$(s)$ is(are) true?
$(A)$ Relative change in the radii of two consecutive orbitals does not depend on $Z$
$(B)$ Relative change in the radii of two consecutive orbitals varies as $1/n$
$(C)$ Relative change in the energy of two consecutive orbitals varies as $1/n^3$
$(D)$ Relative change in the angular momenta of two consecutive orbitals varies as $1/n$

The spectrum obtained from a sodium vapour lamp is an example of