Q. Electron configuration fe.

We want the electron configuration of iron, \( \mathrm{Fe} \).

Step 1: Identify the atomic number of iron.

\( \mathrm{Fe} \) has atomic number \(26\). That means a neutral iron atom has \(26\) electrons total.

Step 2: Fill orbitals in order of increasing energy (the aufbau principle).

For elements up to iron, we fill orbitals in this standard order:

\[
\mathrm{1s,\ 2s,\ 2p,\ 3s,\ 3p,\ 4s,\ 3d}
\]

Step 3: Write the configuration for each shell and subshell.

\[
\begin{aligned}
\mathrm{1s}^2 &: \ 2 \text{ electrons} \\
\mathrm{2s}^2 &: \ 2 \text{ electrons (total }4\text{)} \\
\mathrm{2p}^6 &: \ 6 \text{ electrons (total }10\text{)} \\
\mathrm{3s}^2 &: \ 2 \text{ electrons (total }12\text{)} \\
\mathrm{3p}^6 &: \ 6 \text{ electrons (total }18\text{)} \\
\mathrm{4s}^2 &: \ 2 \text{ electrons (total }20\text{)} \\
\mathrm{3d}^6 &: \ 6 \text{ electrons (total }26\text{)}
\end{aligned}
\]

Step 4: Combine everything into the full electron configuration.

\[
\mathrm{Fe:}\quad 1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^6
\]

Final answer:

\[
\mathrm{Fe = 1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^6}
\]