A gas phase atom with the electronic configuration $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^6$ loses three electrons. What is the electron configuration of the resulting gas phase ion?

Atomic number is iron is 26. Its electronic configuration is 

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^6$. 

So, after loosing three electrons , the electronics configuration becomes $\begin{array}{r}1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^5\end{array}$. 

Hence the option A is correct.