Tollens' reagent confirms the aldehyde group in cis-hex-3-enal

Steps:

• Parse name: "cis-hex-3-enal" indicates a 6-carbon chain with a cis double bond at position 3 and aldehyde (-CHO) at position 1.
• Recognize aldehyde as the key reactive functional group for common test reagents.
• Recall Tollens' reagent oxidizes aldehydes to carboxylic acids, depositing metallic silver.
• Eliminate options by matching reagent specificity to aldehyde reactivity.

Why C is correct:

• Tollens' reagent reacts with aldehydes (RCHO + 2[Ag(NH3)2]+ + 3OH- → RCO2- + 2Ag + 4NH3 + 2H2O), giving a silver mirror test specific for aldehydic carbonyls.

Why the others are wrong:

• A: Sodium borohydride selectively reduces aldehydes to primary alcohols but is a synthetic reagent, not a diagnostic test for identification.
• B: Fehling's reagent tests for reducing sugars (aliphatic aldehydes react, but it's primarily for carbohydrates, not standard for simple aldehydes like this enal).

Final answer: C