Which of the following sequences is correct according to the Aufbau principle?

Identify the correct statements among the following:
$i. E_{2s}(H) > E_{2s}(Li) < E_{2s}(Na) > E_{2s}(K)$
$ii.$ The maximum number of electrons in the shell with principal quantum number $n$ is equal to $2n^2$.
$iii.$ Extra stability of half-filled subshell is due to smaller exchange energy.
$iv.$ Only two electrons,irrespective of their spin,may exist in the same orbital.

How many nodal planes are present in a $d$-orbital?

The atom of the element having atomic number $14$ should have:

For an electron in a $4d$ orbital,which of the following sets of quantum numbers is not possible?

If the period is $6$,then $n = 6$ and $l = 0, 1, 2, 3, 4$. Why is the number of elements in this period still $32$?