Concept:The substance is identified by two tests: reaction with sodium to produce an alkali, and turning white anhydrous copper(II) tetraoxosulphate(VI) blue.
Explanation:Sodium reacts vigorously with water to form sodium hydroxide, which is an alkali, and hydrogen gas.
The reaction is:
2Na+2H2O→2NaOH+H2Also, anhydrous copper(II) tetraoxosulphate(VI),
CuSO4, is white.
When water is added, it becomes hydrated copper(II) tetraoxosulphate(VI),
CuSO4⋅5H2O, which is blue.
Thus, the substance that shows both of these changes is water.
Answer:C. water