The two electrons occupying the same orbital are distinguished by:

Which of the following configurations is correct for iron $(Fe)$?

Which orbital among the following has zero radial nodes and $2$ angular nodes?

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:

Which of the following orbitals is not possible (in $f$)?

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.