NEETChemistryRedox Reactions
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): In the conversion of dichromate ion ( Cr ₂ O ₇²⁻ ) to Cr ³⁺ , the oxidation state of chromium changes from +6 to +3 . Reason (R): The oxidation state of oxygen is -2 in all of its compounds. In the light of the above statements, choose the most appropriate answer from the options given below:
Options
- ABoth (A) and (R) are true and (R) is the correct explanation of (A)
- BBoth (A) and (R) are true but (R) is not the correct explanation of (A)
- C(A) is true but (R) is false
- D(A) is false but (R) is true
Correct answer
C. (A) is true but (R) is false
Step-by-step solution
Assertion (A) is true: Let the oxidation state of Cr in Cr ₂ O ₇²⁻ be x . 2x + 7(-2) = -2 2x - 14 = -2 2x = +12 x = +6 The oxidation state of Cr changes from +6 in Cr ₂ O ₇²⁻ to +3 in Cr ³⁺ . Reason (R) is false: The oxidation state of oxygen is -2 in most of its compounds, but there are exceptions. For example, in peroxides (like H ₂ O ₂ ) it is -1 , in superoxides (like KO ₂ ) it is -1/2 , and in oxygen fluorides (like OF ₂ ) it is +2 . Thus, (A) is true but (R) is false. Answer: (A) is true but (R) is false