Fill in the blanks given below:
$(i)$ The most widely used scale for measuring electronegativity is ........ .
$(ii)$ The similarity observed in periodic properties is known as .............. .
$(iii)$ The elements located in the middle of the periodic table form .......... type of oxides.

The electronic configurations of four elements are $:-$
$(I) \ [Xe] 6s^1$
$(II) \ [Xe] 4f^{14} 5d^1 6s^2$
$(III) \ [Ar] 4s^2 4p^5$
$(IV) \ [Ar] 3d^7 4s^2$
Select the incorrect statement about these elements $:-$

Point out the wrong statement: On moving horizontally from left to right across a period in the periodic table

Which one among the following statements is/are not correct?
$I$. $Ba$ compounds,generally are more covalent than $Be$ compounds.
$II$. The electron gain enthalpy of $He$ is positive.
$III$. The oxidation state of $O$ in $OF_2$ and $Na_2O$ are same.
$IV$. The radius of $Na^{+}$ ion is smaller than that of $F^{-}$ ion.

Which of the following statements are true?
$A.$ Unlike $Ga$ that has a very high melting point,$Cs$ has a very low melting point.
$B.$ On Pauling scale,the electronegativity values of $N$ and $Cl$ are not the same.
$C.$ $Ar$,$K^{+}$,$Cl^{-}$,$Ca^{2+}$,and $S^{2-}$ are all isoelectronic species.
$D.$ The correct order of the first ionization enthalpies of $Na$,$Mg$,$Al$,and $Si$ is $Si > Al > Mg > Na$.
$E.$ The atomic radius of $Cs$ is greater than that of $Li$ and $Rb$.
Choose the correct answer from the options given below

Which of the following statements are correct?
$A.$ The process of the addition of an electron to a neutral gaseous atom is always exothermic.
$B.$ The process of removing an electron from an isolated gaseous atom is always endothermic.
$C.$ The $1^{st}$ ionization energy of boron is less than that of beryllium.
$D.$ The electronegativity of $C$ is $2.5$ in $CH_4$ and $CCl_4$.
$E.$ $Li$ is the most electropositive among elements of group $I$.
Choose the correct answer from the options given below: