Reagent, 1-naphthylamine and sulphanilic acid in acetic acid is used for the detection of:

The reagent consisting of 1-naphthylamine and sulphanilic acid in acetic acid is known as Griess reagent. This is a classic test used for the detection of nitrite ions (NO$$_2^-$$).

In this test, nitrite reacts with sulphanilic acid under acidic conditions to form a diazonium salt. This diazonium salt then couples with 1-naphthylamine to produce a red azo dye, confirming the presence of NO$$_2^-$$.

The answer is $$\boxed{\text{NO}_2^-}$$.