Question

Statement I : Aluminium reacts with excess of \( \mathrm{NaOH} \) to form \( [\mathrm{Al(OH)_6}]^{3-} \)
Statement II : For the complex \( [\mathrm{Fe(H_2O)_6}]^{3+} \) : \( \left[ \left( d_{xy} = d_{yz} = d_{zx} \right) < \left( d_{x^2-y^2} = d_{z^2} \right) \right] \)
and for the complex \( [\mathrm{FeCl_4}]^{2-} \) : \( \left[ \left( d_{xy} = d_{yz} = d_{zx} \right) > \left( d_{x^2-y^2} = d_{z^2} \right) \right] \)

• A. Both Statement I and Statement II are correct
• B. Statement I is correct but Statement II is incorrect.
• C. Statement I is incorrect but Statement II is correct.
• D. Both Statement I and Statement II are incorrect

Hint:

Remember the two key facts: in octahedral complexes, \( t_{2g} \) is lower than \( e_g \), while in tetrahedral complexes the order is reversed. Also, aluminium in excess \( \mathrm{NaOH} \) commonly forms aluminate, \( [\mathrm{Al(OH)_4}]^- \).

Answer 1

The Correct Option is C

Let's analyze each statement to determine their correctness:

1. Statement I: Aluminium reacts with excess of \(\mathrm{NaOH}\) to form \([\mathrm{Al(OH)_6}]^{3-}\)
   • When aluminium reacts with sodium hydroxide (\(\mathrm{NaOH}\)), the usual complex formed is \([\mathrm{Al(OH)_4}]^{-}\), known as a tetrahydroxoaluminate ion.
   • This reaction can be represented as: 

\[\mathrm{2Al + 2NaOH + 6H_2O \rightarrow 2Na[\mathrm{Al(OH)_4}] + 3H_2}\]

• Therefore, the correct complex is \([\mathrm{Al(OH)_4}]^{-}\), not \([\mathrm{Al(OH)_6}]^{3-}\).
• Conclusion: Statement I is incorrect.

1. Statement II: Analysis of the spin states and splitting for complexes \([\mathrm{Fe(H_2O)_6}]^{3+}\) and \([\mathrm{FeCl_4}]^{2-}\)
   • The octahedral complex \([\mathrm{Fe(H_2O)_6}]^{3+}\) involves strong field ligand water which causes splitting such that: \(\left( d_{xy} = d_{yz} = d_{zx} \right) < \left( d_{x^2-y^2} = d_{z^2} \right)\).
   • The tetrahedral complex \([\mathrm{FeCl_4}]^{2-}\) involves weak field ligand chloride which causes splitting such that: \(\left( d_{xy} = d_{yz} = d_{zx} \right) > \left( d_{x^2-y^2} = d_{z^2} \right)\).
   • The pattern is consistent with crystal field splitting for octahedral and tetrahedral complexes.
   • Conclusion: Statement II is correct.

Based on the above analysis, the correct answer is: Statement I is incorrect but Statement II is correct.