Which compound is commonly known as 'Hypo', widely used in photography as a fixing agent to dissolve unexposed silver halides?

💡 Solution & Explanation

Sodium thiosulfate pentahydrate is commonly known as hypo and functions as a fixing agent in photography by dissolving unexposed silver halides to make the image permanent. Other sodium compounds listed serve different industrial or chemical purposes, such as buffering or water softening. Practical chemical applications of common compounds are frequently tested in general science sections.