The principal quantum number of an atom represents:

For $H^{-}$ atom,the energy required for the removal of an electron from various sub-shells is given as under:
The order of the energies would be:

The electrons,identified by quantum numbers $n$ and $l$ as $(i) n = 4, l = 1$,$(ii) n = 4, l = 0$,$(iii) n = 3, l = 2$,$(iv) n = 3, l = 1$,can be placed in order of increasing energy,from the lowest to highest,as:

What are the values of $n$ and $l$ for the $f$-subshell with the lowest energy?

The atomic weight of an element is double its atomic number. If there are four electrons in the $2p$ orbital,the element is:

Number of unpaired electrons in $Fe^{+3}$ $(Z = 26)$ is