How many maximum possible set(s) of quantum no. are possible for $6^{\text{th }}$ electron of Fe?

 The maximum possible set(s) of quantum no. are possible for $6^{\text{th }}$ electron of Fe is 6.

The electronic configuration of Fe is 

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{6}4s^2$ $\mathit{ }\mathit{ }\mathit{(}\mathit{6}th\mathit{ }{e}^{\mathit{-}})$

For 2p orbital

$n=2,l=1,m=+1,0,-1$

The possible  number of sets are

$\begin{array}{l}\Rightarrow n=2,l=1,m=+1,s=\pm \frac{1}{2}\\ n=2,l=1,m=-1,s=\pm \frac{1}{2}\\ n=2,l=1,m=0,s=\pm \frac{1}{2}\end{array}$

From the above observation it is obtained that the maximum possible set(s) of quantum no. are possible for $6^{\text{th }}$ electron of Fe is 6.