The incorrect statement regarding the reaction given below is

Strategy: Analyze the reaction of an aromatic amine with nitrous acid $(\ce{HNO2})$ at low temperature.

Step 1: Reaction details The reaction of N,N-dimethylaniline (an aromatic tertiary amine) with nitrous acid $(\ce{NaNO2 + HCl})$ at low temperature $(0-5 \text{°C})$ results in electrophilic aromatic substitution: $\ce{C6H5N(CH3)2 + HNO2 \to p-ON-C6H4-N(CH3)2 + H2O}$ The product B is p-nitrosodimethylaniline.

Step 2: Statement Analysis

• (a) B is a p-nitroso compound: True.
• (b) B is an N-nitroso ammonium compound: False. N-nitroso compounds are formed from secondary amines. Tertiary amines like this undergo ring nitrosation.
• (c) The reaction occurs at low temperature: True.
• (d) The electrophile is $\ce{NO^+}$: True.

$\boxed{\text{Answer: (Option) [b] 'B' is N-nitroso ammonium compound}}$