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 $\mathrm{eV} {\mathrm{atom}}^{-1}$.

Which of the following statements are true and false?

${\mathrm{S}}_1: {\mathrm{IE}}_1$ of $\mathrm{Sr}>\mathrm{Rb}$ but ${\mathrm{IE}}_2$ for $\mathrm{Rb}>\mathrm{Sr}$.

${\mathrm{S}}_2:$ The ionic radii of ${\mathrm{Li}}^{+}, {\mathrm{K}}^{+}, {\mathrm{Mg}}^{2+}$and ${\mathrm{Al}}^{3+}$ in $\mathrm{Å}$ are $0.76, 1.38, 0.720$ and $0.535,$ respectively.

${\mathrm{S}}_3:$ The negative value of electron gain enthalpy of $\mathrm{Cl}>\mathrm{F}$ because there is weak electron-electron repulsion in a bigger $3\mathrm{p}$ subshell of $\mathrm{Cl}$  as compared to compact $2\mathrm{p}$ subshell of $\mathrm{F}$.

${\mathrm{S}}_4:$ The second ionization energy of copper is less than potassium.