Which of the following represents the wavelength of spectral line of Balmer series of $\mathrm{He}^{+}$ion?

$(R=$ Rydberg constant, $n>2)$

The work functions (in eV ) of $\mathrm{Mg}, \mathrm{Cu}, \mathrm{Ag}, \mathrm{Na}$ respectively are $3.7,4.8,4.3,2.3$. From how many metals, the electrons will be ejected if their surfaces are irradiated with an electromagnetic radiation of wavelength 300 nm ?

$\left(h=6.6 \times 10^{-34} \mathrm{Js}, 1 \mathrm{eV}=1.6 \times 10^{-19} \mathrm{~J}\right)$

The order of negative electron gain enthalpy of $\mathrm{Li}, \mathrm{Na}$, $\mathrm{S}, \mathrm{Cl}$ is

The number of molecules having lone pair of electrons on central atom in the following is

$\mathrm{BF}_3, \mathrm{SF}_4, \mathrm{SiCl}_4, \mathrm{XeF}_4, \mathrm{NCl}_3, \mathrm{XeF}_6, \mathrm{PCl}_5, \mathrm{HgCl}_2, \mathrm{SnCl}_2$