The radius of $3^{rd}$ orbit of hydrogen atom is $R \text{ pm}$. The radius of $2^{nd}$ orbit of $He^{+}$ ion (in $\text{pm}$) is

$(i)$ What is the energy of an electron for hydrogen in $J \ atom^{-1}$ and $J \ mol^{-1}$?
$(ii)$ Calculate the energy of this electron per mole for the first transition ($n=1$ to $n=2$).
$(iii)$ Calculate the ionization energy of hydrogen.

The electronic transitions from $n=2$ to $n=1$ will produce the shortest wavelength in which of the following species? (where $n$ is the principal quantum state)

When an electron jumps from $n = 5$ to $n = 2$ with all possible transitions,which of the following statements is correct?

For which of the following species,Bohr's theory is not applicable?

Values of work function $(W_0)$ for a few metals are given below:

Metal	$Li$	$Na$	$K$	$Mg$	$Cu$	$Ag$
$W_0 / eV$	$2.42$	$2.3$	$2.25$	$3.7$	$4.8$	$4.3$

The number of metals which will show photoelectric effect when light of wavelength $400 \ nm$ falls on it is $........$.
Given: $h = 6.6 \times 10^{-34} \ J \ s$,$c = 3 \times 10^8 \ m \ s^{-1}$,$e = 1.6 \times 10^{-19} \ C$