The incorrect statement regarding the reaction given below is

Explanation

The starting compound is $$N,N$$-dimethylaniline, which is a tertiary aromatic amine.

In the presence of $$NaNO_2$$ and mineral acid $$HX$$, nitrous acid is generated in situ.

$$NaNO_2 + HX \rightarrow HNO_2$$

In acidic medium, nitrous acid generates the nitrosonium ion:

$$HNO_2 + H^+ \rightarrow NO^+ + H_2O$$

The electrophile in this reaction is:

$$NO^+$$

Since the $$-N(CH_3)_2$$ group is strongly electron-donating, it activates the benzene ring towards electrophilic substitution.

Due to steric hindrance, substitution occurs predominantly at the para position to give $$p$$-nitroso-$$N,N$$-dimethylaniline.

Statement A is correct because the product formed is the para-nitroso derivative of $$N,N$$-dimethylaniline.

Statement C is correct because nitrous acid is unstable at room temperature. Therefore, the reaction is carried out at low temperature, typically $$0^\circ\text{C}$$ to $$5^\circ\text{C}$$.

Statement D is correct because the electrophile responsible for the reaction is the nitrosonium ion:

$$NO^+$$

Statement B is incorrect.

Secondary amines undergo $$N$$-nitrosation to form $$N$$-nitrosoamines.

Tertiary aromatic amines do not undergo $$N$$-nitrosation because the nitrogen atom has no replaceable hydrogen.

Instead, they undergo $$C$$-nitrosation on the aromatic ring to form para-nitroso substituted products.

Hence, the stable product is a $$C$$-nitroso compound and not an $$N$$-nitroso ammonium compound.

Therefore, the incorrect statement is Option B.