In the nitrate test, which reagents produce a red color indicating nitrite production?

In the nitrate test, which reagents produce a red color indicating nitrite production?

• A. Alpha-naphthol and potassium hydroxide
• B. p-Dimethylaminobenzaldehyde and amyl alcohol
• C. Ninhydrin and acetone
• D. Alpha-naphthylamine and sulfanilic acid

Answer: (D)

In the nitrate test, nitrite produced by bacterial reduction is detected by the Griess reaction. Nitrite reacts with sulfanilic acid to form a diazonium salt, which then couples with alpha-naphthylamine to create a red azo dye. That red color signals nitrite presence, confirming nitrate reduction. The pair of reagents shown are the classic Griess reagents specifically chosen to produce that red dye, whereas the other reagent combinations are used in different color reactions or do not yield the characteristic red azo dye with nitrite, so they don’t indicate nitrite production in this test.

In the nitrate test, nitrite produced by bacterial reduction is detected by the Griess reaction. Nitrite reacts with sulfanilic acid to form a diazonium salt, which then couples with alpha-naphthylamine to create a red azo dye. That red color signals nitrite presence, confirming nitrate reduction. The pair of reagents shown are the classic Griess reagents specifically chosen to produce that red dye, whereas the other reagent combinations are used in different color reactions or do not yield the characteristic red azo dye with nitrite, so they don’t indicate nitrite production in this test.