MCQ Detailed View

In photography, after a photographic film or paper is exposed to light, a latent image is formed that is invisible. To make this image permanent and stable, it must be treated with a fixer chemical, which removes unexposed silver halide crystals from the film. The most commonly used fixer in photography is sodium thiosulphate, often called “hypo”.

Sodium thiosulphate works by dissolving the unexposed silver halide, leaving behind the metallic silver that forms the visible image. This process ensures that the photographic image does not darken further when exposed to light, making it permanent. The chemical reaction can be summarized as:

AgBr (unexposed) + 2 Na₂S₂O₃ → Na₃[Ag(S₂O₃)₂] + NaBr

This reaction forms a soluble complex that can be washed away, while the image created by exposed silver remains intact.

Other chemicals listed, such as sodium sulphate, borax, or ammonium sulphate, are not used as photographic fixers. Sodium sulphate is used in industry as a drying agent, borax is commonly used in cleaning and glassmaking, and ammonium sulphate is mainly used in fertilizers.

Understanding the use of sodium thiosulphate as a fixer is essential in chemistry and everyday science, as it links chemical reactions with practical applications. It also demonstrates how chemistry plays a crucial role in image processing, photography, and visual arts, showing real-life applications of inorganic chemistry in daily life.