Which of the following \(f\)-block element exhibits the highest oxidation state?
Show Hint
The highest commonly observed oxidation state among the early actinides is \(+7\), shown by neptunium in compounds such as \(Np_2O_5\) and related species.
Step 1: Recall the oxidation states of actinides.
Actinides exhibit a wide range of oxidation states because the energies of \(5f\), \(6d\), and \(7s\) orbitals are comparable.
Hence, several electrons can participate in bonding.
Step 2: Examine the given elements.
For uranium:
\[
\text{Maximum oxidation state}=+6
\]
For protactinium:
\[
\text{Maximum oxidation state}=+5
\]
For americium:
\[
\text{Maximum oxidation state}=+6
\]
For neptunium:
\[
\text{Maximum oxidation state}=+7
\]
Step 3: Compare the oxidation states.
Among the given elements:
\[
Np(+7) \gt U(+6) = Am(+6) \gt Pa(+5)
\]
Thus, neptunium exhibits the highest oxidation state.
Step 4: Final conclusion.
Therefore, the \(f\)-block element exhibiting the highest oxidation state is
\[
\boxed{Np}
\]
Hence, the correct option is
\[
\boxed{(2)}
\]