The first ionization enthalpies of $\mathrm{Be}, \mathrm{B}, \mathrm{N}$ and $\mathrm{O}$ follow the order

The total number of acidic oxides from the following list is:

$\mathrm{NO}, {\mathrm{N}}_2\mathrm{O}, {\mathrm{B}}_2{\mathrm{O}}_3,{ \mathrm{N}}_2{\mathrm{O}}_5, \mathrm{CO}, {\mathrm{SO}}_3, {\mathrm{P}}_4{\mathrm{O}}_{10}$

Given two statements below :

Statement I : In ${\mathrm{Cl}}_2$ molecule the covalent radius is double of the atomic radius of chlorine.

Statement II : Radius of anionic species is always greater than their parent atomic radius.

Choose the most appropriate answer from options given below 

Outermost electronic configurations of four elements $\mathrm{A},\mathrm{B},\mathrm{C},\mathrm{D}$ are given below:

(A) $3{\mathrm{s}}^2$

(B) $3{\mathrm{s}}^{2}3{\mathrm{p}}^1$

(C) $3{\mathrm{s}}^2 3{\mathrm{p}}^3$

(D) $3{\mathrm{s}}^2 3{\mathrm{p}}^4$

The correct order of first ionisation enthalpy for them is

In which of the following pairs, electron gain enthalpies of constituent elements are nearly the same or identical?

(A) $\mathrm{Rb}$ and $\mathrm{Cs}$

(B) $\mathrm{Na}$ and $\mathrm{K}$

(C) $\mathrm{Ar}$ and $\mathrm{Kr}$

(D) $\mathrm{I}$ and $\mathrm{At}$

Choose the correct answer from the options given below:

It is observed that characteristic X-ray spectra of elements show regularity. When frequency to the power 'n' i.e. ${\mathrm{v}}^{\mathrm{n}}$ of X-rays emitted is plotted against atomic number $\mathrm{Z}$, the following graph is obtained.

The value of 'n' is