Which element from the following exhibits a diagonal relationship with $Mg$?

Which of these does not reflect the periodicity of the elements?

Which of the following set of properties generally decreases along a period?

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 correct order of first ionization enthalpy values of $Li, Na, F$ and $Cl$ is $Na < Li < Cl < F$.
Statement $II$ : The correct order of negative electron gain enthalpy values of $Li, Na, F$ and $Cl$ is $Na < Li < F < Cl$.
In the light of the above statements,choose the correct answer from the options given below :

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