Fill in the missing reagent for the provided reaction.

• A.
• B.
• C.
• D.

Answer: (D)

Verified step by step guidance

1. Step 1: Identify the type of reaction shown in the images. The reaction involves benzene undergoing substitution to introduce a nitro group (NO2) onto the aromatic ring, which is characteristic of an electrophilic aromatic substitution (EAS) reaction called nitration.
2. Step 2: Recognize that nitration of benzene requires a nitronium ion (NO2+) as the electrophile. This electrophile is generated in situ by reacting concentrated nitric acid (HNO3) with concentrated sulfuric acid (H2SO4).
3. Step 3: Write the reagent mixture needed to generate the nitronium ion: a mixture of concentrated nitric acid and concentrated sulfuric acid, often represented as HNO3 / H2SO4.
4. Step 4: Understand the mechanism: sulfuric acid protonates nitric acid, leading to the loss of water and formation of the nitronium ion (NO2+), which then attacks the benzene ring to form the nitrobenzene intermediate.
5. Step 5: Conclude that the missing reagent in the reaction is the nitrating mixture of concentrated nitric acid and concentrated sulfuric acid, which facilitates the electrophilic aromatic substitution to produce nitrobenzene.