Réponse :Chemical indicator, any substance that gives a visible sign, usually by a colour change, of the presence or absence of a threshold concentration of a chemical species, such as an acid or an alkali in a solution. An example is the substance called methyl yellow, which imparts a yellow colour to an alkaline solution. there is different types of indicators which are economic indicators, depending on their timing: leading, lagging, and coincident indicators.
Explications :
