The ionization potential of hydrogen atom is $13.6 \ eV$. The energy required to remove an electron from the $n = 2$ state of hydrogen atom is : ............ $eV$

What is the energy associated with the first orbit of $Li^{2+}$ $(R_{H} = 2.18 \times 10^{-18} \ J)$?

How many emission spectral lines are possible when a hydrogen atom is excited to the $n$th energy level?

Given below are two statements.
Statement $I:$ According to Bohr's model of an atom,qualitatively the magnitude of velocity of electron increases with decrease in positive charges on the nucleus as there is no strong hold on the electron by the nucleus.
Statement $II:$ According to Bohr's model of an atom,qualitatively the magnitude of velocity of electron increases with decrease in principal quantum number.
In the light of the above statements,choose the most appropriate answer from the options given below:

Following results are observed when sodium metal is irradiated with different wavelengths. Calculate $(a)$ threshold wavelength and $(b)$ Planck's constant.

$\lambda \ (nm)$	$500, 450, 400$
$v \times 10^{-5} \ (cm \ s^{-1})$	$2.55, 4.35, 5.35$

What is the name by which Thomson's atomic model is known?