NEET 2020 · ChemistryOxidation statePrevious Year Question

Identify the incorrect statement.

Answer: (B) (b) The oxidation states of chromium in $CrO X_{4} X^{2 -}$ and $Cr X_{2} O X_{7} X^{2 -}$ are not the same.. \textbf{Answer:} (b) The oxidation states of chromium in $CrO X_{4} X^{2 -}$ and $Cr X_{2} O X_{7} X^{2 -}$ are not the same.

A.(a) Interstitial compounds are those that are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals.
B.(b) The oxidation states of chromium in $CrO X_{4} X^{2 -}$ and $Cr X_{2} O X_{7} X^{2 -}$ are not the same.✓
C.(c) $Cr X^{2 +}$ ( $d X^{4}$ ) is a stronger reducing agent than $Fe X^{2 +}$ ( $d X^{6}$ ) in water.
D.(d) 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.

Correct Answer

(B) (b) The oxidation states of chromium in $CrO X_{4} X^{2 -}$ and $Cr X_{2} O X_{7} X^{2 -}$ are not the same.

Solution & Explanation

\textbf{Answer:} (b) The oxidation states of chromium in $CrO X_{4} X^{2 -}$ and $Cr X_{2} O X_{7} X^{2 -}$ are not the same. (This is the incorrect statement.) \textbf{Solution:} In both $CrO X_{4} X^{2 -}$ and $Cr X_{2} O X_{7} X^{2 -}$ chromium is in the $+ 6$ oxidation state, so the statement that they are "not the same" is wrong — making (b) the incorrect statement. The others are correct: (a) interstitial compounds do form by trapping small H, C, N atoms in metal lattices; (c) $Cr X^{2 +}$ is a stronger reducing agent than $Fe X^{2 +}$ because oxidation of $Cr X^{2 +}$ gives the stable $d X^{3}$ $Cr X^{3 +}$ ; (d) transition metals catalyse reactions through variable oxidation states and complex formation. Hence the incorrect statement is (b).

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