Color changes in ethanol reactions

Steps:

• First reaction oxidizes ethanol to ethanal using acidified dichromate (Cr₂O₇²⁻), changing from orange to green as Cr(VI) reduces to Cr(III).
• Second reaction has sodium dissolving in ethanol to form sodium ethoxide and hydrogen, with sodium changing from metallic silver to dull grey/white.
• Option A matches both reactions showing visible color changes in reagents.
• Options B, C, D contain factual errors on products, catalysis, and reaction type.

Why A is correct:

• Oxidation with dichromate follows Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O, causing orange-to-green color shift; sodium reaction is 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂, with sodium surface discoloration.

Why the others are wrong:

• B: Ethanol is the starting material, not formed; dichromate oxidizes it, doesn't catalyze its production.
• C: Reaction uses acidified Cr₂O₇²⁻ (dichromate ion) as oxidant, not catalyst; "potassium" is unspecified and incorrect for catalysis.
• D: Sodium ethoxide forms via metal-alcohol displacement, not dehydration (which eliminates water to yield ethene).

Final answer: A