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.

In a period, the first ionisation enthalpy of the element at the extreme left and the negative electron gain enthalpy of the extreme right element, except noble gases, are respectively.

Given below are two statements :
Statement $I$ : $K > Mg > Al > B$ is the correct order in terms of metallic character.
Statement $II$ : Atomic radius is always greater than the ionic radius for any element.
In the light of the above statements, choose the correct answer from the options given below

Which one of the following sets of ions represents a collection of isoelectronic species?

Match the Column $I$ with Column $II$ and select the correct answer using the given codes.

Column $I$ (Element types)	Column $II$ (Electronic configuration)
$A$. Inert-gas elements	$1. (n-1)d^{1-10} ns^{1-2}$
$B$. Transition elements	$2. ns^2 np^6$
$C$. Inner-transition elements	$3. (n-2)f^{1-14} (n-1)s^2 p^6 d^{0-1} ns^2$

Given below are two statements $:$
Statement $(I) :$ The radii of isoelectronic species increase in the order $Mg^{2+} < Na^{+} < F^{-} < O^{2-}$.
Statement $(II) :$ The magnitude of electron gain enthalpy of halogens decreases in the order $Cl > F > Br > I$.
In the light of the above statements,choose the most appropriate answer from the options given below $:$