The total spin of an iron $(Fe)$ atom is .......

The quantum numbers $n$ and $l$ for four electrons are given as: $(1) \, n = 4, l = 1; \, (2) \, n = 4, l = 0; \, (3) \, n = 3, l = 2; \, (4) \, n = 3, l = 1$. Arrange them in increasing order of their energy.

The number of correct statements from the following:
$A.$ For $1s$ orbital,the probability density is maximum at the nucleus.
$B.$ For $2s$ orbital,the probability density first increases to maximum and then decreases sharply to zero.
$C.$ Boundary surface diagrams of the orbitals enclose a region of $100\%$ probability of finding the electron.
$D.$ $p$ and $d$-orbitals have $1$ and $2$ angular nodes respectively.
$E.$ Probability density of $p$-orbital is zero at the nucleus.

Identify the incorrect statement from the following:

How many electrons can be fit into the orbitals that comprise the $3^{rd}$ quantum shell $(n = 3)$?

Which of the following represents the ground state electronic configuration of an atom?