hydrogen bromide is not the electrophile its bromide ion may act as the nucleophile, in alkyl halide the alkyl group may act as an electrophile.

NO2+ is.

Indicator will changes the colour according to H+ ion present in a solution.

Reagent : consist of electrophile and nucleophile. It help in the attachment of nucleophile to the electrophile and electrophile to the nucleophile.

Mirza

In Reimer- Tieman reaction the electrophile is dichlorocarbene

The positive species which may attack on carbon or a pi bonds are electrophile as Cl+, NO2+ etc. but H+ and Positive metallic ions are not electrophile .