Which of the following represents a redox reaction?

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Multiple Choice

Which of the following represents a redox reaction?

Redox reactions involve a transfer of electrons, with one species being oxidized (oxidation state increases) and another being reduced (oxidation state decreases). In CuS + H2 → H2S + Cu, hydrogen starts as H2 (oxidation state 0) and ends up as part of H2S where hydrogen is +1. That means H2 is oxidized. Copper in CuS is +2 and ends as metallic Cu (0), so copper is reduced. Sulfur stays at -2 throughout. This gives a clear, paired electron transfer: H2 gives electrons to CuS, reducing copper while oxidizing hydrogen. The other reactions don’t show a straightforward paired redox in the written form. For the second option, copper would be reduced without a clear counterpart being oxidized in that same step. The last two options involve redox processes too, but they are less transparent as single, simple redox couples in the equation as written.

Redox reactions involve a transfer of electrons, with one species being oxidized (oxidation state increases) and another being reduced (oxidation state decreases).

In CuS + H2 → H2S + Cu, hydrogen starts as H2 (oxidation state 0) and ends up as part of H2S where hydrogen is +1. That means H2 is oxidized. Copper in CuS is +2 and ends as metallic Cu (0), so copper is reduced. Sulfur stays at -2 throughout. This gives a clear, paired electron transfer: H2 gives electrons to CuS, reducing copper while oxidizing hydrogen.

The other reactions don’t show a straightforward paired redox in the written form. For the second option, copper would be reduced without a clear counterpart being oxidized in that same step. The last two options involve redox processes too, but they are less transparent as single, simple redox couples in the equation as written.

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