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NEET CHEMISTRYEasy

The correct order of increasing field strength of ligands is:

A

SCN−<F−<CN−<C2O42−SCN^- < F^- < CN^- < C_2O_4^{2-}

B

F−<SCN−<C2O42−<CN−F^- < SCN^- < C_2O_4^{2-} < CN^-

C

CN−<C2O42−<SCN−<F−CN^- < C_2O_4^{2-} < SCN^- < F^-

D

SCN−<F−<C2O42−<CN−SCN^- < F^- < C_2O_4^{2-} < CN^-

Step-by-Step Solution

The crystal field splitting energy (Δo\Delta_o) depends on the nature of the ligand. Ligands are arranged in a series called the spectrochemical series based on the increasing order of the field strength they produce.

According to the NCERT textbook, the order is: I−<Br−<SCN−<Cl−<S2−<F−<OH−<C2O42−<H2O<NCS−<edta4−<NH3<en<CN−<COI^- < Br^- < SCN^- < Cl^- < S^{2-} < F^- < OH^- < C_2O_4^{2-} < H_2O < NCS^- < edta^{4-} < NH_3 < en < CN^- < CO

Comparing the specific ligands given in the options:

  1. SCN−SCN^- (thiocyanate) is a weak field ligand (appearing early in the series).
  2. F−F^- (fluoride) is a weak field ligand but stronger than SCN−SCN^-.
  3. C2O42−C_2O_4^{2-} (oxalate) is stronger than F−F^- (it produces a larger splitting).
  4. CN−CN^- (cyanide) is a very strong field ligand (appearing near the end of the series).

Therefore, the correct increasing order is SCN−<F−<C2O42−<CN−SCN^- < F^- < C_2O_4^{2-} < CN^- .

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