Identify the incorrect statement.

• A

  The transition metals and their compounds are known for their catalytic activity due to their ability to adopt multiple oxidation states and to form complexes.
• B

  Interstitial compounds are those that are formed when small atoms like $\mathrm{H},\mathrm{C}$ or $\mathrm{N}$ are trapped inside the crystal lattices of metals.
• Correct answer
  C

  The oxidation states of chromium in ${\mathrm{CrO}}_4^{2-}$ and ${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}$ are not the same.
• D

  ${\mathrm{Cr}}_2+\left({\mathrm{d}}^4\right)$ is a stronger reducing agent than ${\mathrm{Fe}}^{2+}+\left({\mathrm{d}}^6\right)$ in water.

Hence, the correct answer is option: 'C'.