The ionization energy of ${\mathrm{He}}^{+}$ is $19.6\times {10}^{-18} \mathrm{J} {\mathrm{atom}}^{-1}.$ The energy of the first stationary state $(\mathrm{n}=1)$ of ${\mathrm{Li}}^{2+}$ is:

The energy of an electron in a hydrogen-like is given by ${\mathrm{E}}_{\mathrm{n}}=-\left(2.18\times {10}^{-18}\right)\left(\frac{{\mathrm{Z}}^2}{{\mathrm{n}}^2}\right).$

Whereas: $\mathrm{n}$ is the principal quantum number and $\mathrm{Z}$ is the atomic number of the element.

The ionization energy (in $\mathrm{kJ} {\mathrm{mol}}^{-1}$) of the ${\mathrm{Li}}^{2+}$ ion is

Atomic numbers of some elements are given below. The number of elements from the following that will be placed in group $2$ of the modern periodic table is________.

$3, 4, 7, 12, 18, 20, 26, 32, 38$

The number of elements from the following which have valence electron(s) in the $\mathrm{M}$-shell is_______.

$\mathrm{Si}, \mathrm{C}, \mathrm{N}, \mathrm{Be}, \mathrm{Al}, \mathrm{S}, \mathrm{F}, \mathrm{B}, \mathrm{Li}, \mathrm{Mg}, \mathrm{O}, \mathrm{Ar}$

How many of the following elements are more electronegative than Boron.

(i) $\mathrm{H}$ (ii) $\mathrm{Li}$ (iii) $\mathrm{Be}$ (iv) $\mathrm{C}$ (v) $\mathrm{N}$ (vi) $\mathrm{O}$ (vii) $\mathrm{F}$

The amount of energy released when ${10}^{12}$ atoms of $\mathrm{Cl}$ vapours are converted into ${\mathrm{Cl}}^{-}$ ions according to the equation $\mathrm{Cl} \left(\mathrm{g}\right)+{\mathrm{e}}^{-}⟶{\mathrm{Cl}}_{}^{-} \left(\mathrm{g}\right)$ is $58\times {10}^{-10} \mathrm{J}$. Calculate ${\mathrm{\Delta }}_{\mathrm{eg}}\mathrm{H}$ of $\mathrm{Cl}$ atom in $\mathrm{kJ} {\mathrm{mol}}^{-1}$ or $\mathrm{eV} {\mathrm{atom}}^{-1}$.