Which of the following methods is NOT used  for the separation of mixtures?

Step 1: Analyze the question We need the one process that is not a standard method of separating mixtures.

Step 2: Review the concepts Separation techniques use physical differences between components in a mixture:

• Chromatography: separates substances by their different rates of movement through a medium. It is used for mixtures like inks, dyes and plant pigments.
• Crystallization: separates a dissolved solid from its solution by evaporating the solvent so crystals form. Example: obtaining salt from brine.
• Distillation: separates liquids by their different boiling points, or a solvent from a solution. Example: ethanol from water, or fractional distillation of crude oil.
• Electrolysis: breaks down an ionic compound, in molten or solution form, into its elements by passing an electric current through it. It is a chemical decomposition, not a physical separation of a mixture. It is used for extracting metals (e.g. aluminium), electroplating and refining copper.

Step 3: Apply to the options A, B and C are all physical separation techniques for mixtures. Electrolysis decomposes a compound, which is a chemical change, so it is not a mixture-separation method in the usual sense.

Step 4: Answer The correct option is D. Electrolysis.

Exam tip: Separation of mixtures is a physical process, using properties like boiling point, solubility, or particle size. Electrolysis breaks chemical bonds in a compound, so it is not a separation method. Remember: "Mixtures are separated; compounds are decomposed."