Light,a well-known form of energy,is treated as a form of matter,by saying that it consists of:

The radius of the $2^{nd}$ orbit of $Li^{2+}$ is $x$. The expected radius of the $3^{rd}$ orbit of $Be^{3+}$ is:

What is the wavelength of light required to raise an electron in the $O^{7+}$ ion from $n=1$ shell to $n=2$ shell in $nm$?

Which of the following statements are correct?
$I$) The energy of hydrogen atom in its ground state is $-13.6 \ eV$
$II$) On the basis of Bohr's model,the radius of the $3^{rd}$ orbit of hydrogen atom is $158.7 \ pm$
$III$) The order of radius of the first orbit of $H, He^{+}, Li^{2+}$ and $Be^{3+}$ is $H > He^{+} > Li^{2+} > Be^{3+}$

The energy required by electrons,present in the first Bohr orbit of hydrogen atom to be excited to the second Bohr orbit is . . . . . . $J \ mol^{-1}$.
Given: $R_{H} = 2.18 \times 10^{-11} \ ergs$

The surface of sodium metal is irradiated with radiation of wavelength $x$ nm. The kinetic energy of ejected electrons is $2.8 \times 10^{-20}$ $J$. The work function of sodium is $2.3$ eV. The value of $x$ is . . . . . . $\times 10^2$ nm.