In a mixture of two compounds, if both compounds have similar properties, which technique is least effective for separation?

In a mixture of two compounds with similar properties, such as boiling points or polarity, simple distillation is least effective for separation.

Simple distillation relies on the difference in boiling points to separate components—if the compounds have close boiling points, this technique will not achieve effective separation. The close proximity of their boiling points means they will vaporize and condense together, making it difficult to isolate one from the other.

In contrast, fractional distillation is designed to enhance the separation of components with small differences in boiling points by using a fractionating column, allowing for multiple vaporization-condensation cycles that improve purity. Similarly, column chromatography can effectively separate compounds based on differences in polarity or size, even when the compounds are similar. Steam distillation is useful for separating compounds with high boiling points and can be effective for certain types of mixtures; however, its suitability would depend on the compounds involved.

Thus, among the techniques listed, simple distillation is the least effective for separating compounds with similar properties due to its reliance on significant differences in boiling points.