Redox reactions require both oxidation and reduction

Steps:

• Define oxidation as loss of electrons (or gain of oxygen/loss of hydrogen) and reduction as gain of electrons (or loss of oxygen/gain of hydrogen).
• Recognize that oxidation and reduction are paired processes in redox reactions, as electrons transferred in one must be accepted in the other.
• Evaluate each option against these definitions to identify the accurate statement.
• Confirm B aligns with the fundamental principle that no oxidation occurs without a corresponding reduction.

Why B is correct:

• In redox reactions, oxidation (electron loss) always pairs with reduction (electron gain), ensuring charge balance as per the law of conservation of electrons.

Why the others are wrong:

• A: Acidified manganate(VII) ions are purple and turn colourless (not from colourless to purple) when reduced to Mn²⁺.
• C: Oxidising agents gain electrons (they cause oxidation in other species by accepting electrons).
• D: Reduction is gain of hydrogen (or loss of oxygen); loss of hydrogen defines oxidation.

Final answer: B