If in Bohr's model,for a unielectronic atom,the time period of revolution is represented as $T_{n,Z}$ where $n$ represents the shell number and $Z$ represents the atomic number,then the value of $T_{1,2} : T_{2,1}$ will be

Light of frequency $1.6 \times 10^{16} \ Hz$ falling on a metal plate emits electrons that have double the kinetic energy compared to the kinetic energy of electrons emitted when light of frequency $1.0 \times 10^{16} \ Hz$ falls on the same plate. The threshold frequency $(v_0)$ of the metal in $Hz$ is:

Match the following for hydrogen atom $(Z=1)$ :-

$(P). \lambda_{\max }$ in Lyman series	$(i). \infty \rightarrow 1$
$(Q). v_{\min }$ in Balmer series	$(ii). 2 \rightarrow 1$
$(R). \lambda_{\min }$ in Lyman series	$(iii). 3 \rightarrow 2$
$(S). v_{\max }$ in Balmer series	$(iv). \infty \rightarrow 2$

In the Bohr model of the atom,when an electron undergoes a transition from $n = 1$ to $n = 3$,the energy absorbed or emitted is ........

The shortest wavelength of $He^{+}$ ion in Balmer series is $x$. Then,the longest wavelength in the Paschen series of $Li^{2+}$ is:

In a photoelectric effect experiment, the kinetic energy of an emitted electron is $1.986 \times 10^{-19} \ J$, when a radiation of frequency $1.0 \times 10^{15} \ s^{-1}$ hits the metal. What is the threshold frequency of the metal (in $s^{-1}$)? (Planck's constant $= 6.62 \times 10^{-34} \ J \ s$)