To determine whether a substance is a strong electrolyte, the key factor is its ability to dissociate completely into ions when dissolved in water. Therefore, the correct answer is:
b) dissociate virtually completely to its ions in solution.
A strong electrolyte is characterized by its ability to produce a large number of ions that can conduct electricity effectively. While many strong electrolytes are ionic compounds, simply being an ionic compound does not guarantee that it will behave as a strong electrolyte. Some ionic compounds are poorly soluble in water and thus do not produce significant ionic dissociation. Furthermore, the presence of both metal and nonmetals, as suggested in option d), is common in ionic compounds, but again, this alone does not define the strength of an electrolyte.
In summary, for a substance to be classified as a strong electrolyte, it must dissociate almost completely into its ions in solution, making option b the most accurate choice.