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MCAT Chemistry Question — Reduction & Oxidation

What is the identity of the reducing agent and oxidizing agent, respectively, in the reaction shown below?

2Cr(OH)3 + 3H2O2 + 4NaOH → 2Na2CrO4 + 8H2O

  1. Cr(OH)3  and NaOH
  2. Cr(OH)3 and H2O2
  3. H2O2 and Cr(OH)3
  4. H2O2 and NaOH
Click for Explanation

To answer this question, you must identify the atom that is reduced and the atom that is oxidized. In the reaction above, chromium is oxidized from +3 to +6, which makes chromium hydroxide the reducing agent. Alternatively, oxygen in hydrogen peroxide is reduced from -1 to -2, which makes it the oxidizing agent. Thus, the correct answer is B.

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