Which of the following is not a periodic property?

Which of the following orders is correct according to the given property?

Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However,oxygen has lower ionisation enthalpy than nitrogen. Explain.

Which of the following statements are correct?
$(i)$ First ionisation enthalpy of $He < $ Second ionisation enthalpy of $Li$.
$(ii)$ $Li$ has the highest second ionisation enthalpy.
$(iii)$ All $d$-block elements are transition elements.
$(iv)$ The only alphabet not found in the periodic table is the letter '$J$'.
$(v)$ Francium concentration is $\sim 10^{-18} \ ppm$ on Earth.

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.

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.