Answer: Option (a) is the correct answer.
Explanation:
A property which can be observed when the chemical composition of the substance changes is referred to as chemical property.
For example, melting point, acidity, basicity, boiling point etc are all chemical properties of a substance.
In the given options, it's a white crystalline powder, it can dissolve in water and it can be separated from water by distillation, these all represent the physical property and no change in the chemical composition of soda ash.
Thus, we can conclude that it's a highly basic substance is a chemical property of soda ash.