What is the total number of unpaired electrons in an element placed at period-$4$ and group-$12$ either in excited or at ground state?

Which of the following is/are not correct with respect to energy of atomic orbitals of hydrogen atom?
$A$. $1s < 2p < 3d < 4s$
$B$. $1s < 2s = 2p < 3s = 3p$
$C$. $1s < 2s < 2p < 3s < 3p$
$D$. $1s < 2s < 4s < 3d$
Choose the correct answer from the options given below:

The electronic configurations of ${}_{24}Cr$ and ${}_{29}Cu$ are abnormal because $:-$

Which one is the electronic configuration of $Fe^{2+}$?

For $n = 3$ energy level,the number of possible orbitals (all kinds) are

The correct decreasing order of energy for the orbitals having the following set of quantum numbers:
$A$. $n=3, \ell=0, m=0$
$B$. $n=4, \ell=0, m=0$
$C$. $n=3, \ell=1, m=0$
$D$. $n=3, \ell=2, m=1$