There are various ways to tell two elements apart from each other, but two common methods are:
1. Physical properties: Each element has unique physical properties that can be used to differentiate it from others. For example, elements can have different colors, densities, melting points, boiling points, and solubility in various solvents. Observing these physical properties can help distinguish one element from another.
2. Chemical properties: Elements can be identified by their chemical properties, including their reactivity, the types of compounds they form, and their behavior during chemical reactions. For example, the reaction of an element with acid or with other compounds can be used to identify it. Also, some elements exhibit unique spectral characteristics when heated or exposed to light, which can be used to identify them.