In grouping substances based on their physical properties in the given activity, the first step is likely to be the observation and identification of distinctive properties. These properties may include characteristics like color, odor, density, melting point, boiling point, solubility, and others. By systematically observing and comparing these physical properties, substances can be categorized or grouped based on similarities or differences. This initial step lays the foundation for organizing and classifying substances according to their shared or unique physical attributes, providing a basis for further analysis and understanding of their chemical and physical behavior.