Which of the following pairs shows diagonal relationship?

Among the following, the pair of elements having same electronegativity values are

I. H and $\mathrm{P} \quad$ II. Be and Al III. N and $\mathrm{Cl} \quad$ IV. C and P

Based on the quantum numbers, what will be the maximum number of element for sixth period of the periodic table?

Assertion (A) $\mathrm{Mg}^{2+}$ and $\mathrm{Al}^{3+}$ are isoelectronic but the magnitude of ionic radius of $\mathrm{Al}^{3+}$ is less than that in $\mathrm{Mg}^{2+}$.

Reason (R) The effective nuclear charge on the outermost electrons in $\mathrm{Al}^{3+}$ is greater than that in $\mathrm{Mg}^{2+}$.The correct option among the following is