JAMB Chemistry 1983 Question 33

In the preparation of some pure crystals of Cu(NO₃)₂ starting with CuO, a student gave the following statements as steps he employed. Which of these shows a flaw in his report?

1. A.Some CuO was reacted with excess dilute H₂SO₄.
2. B.The solution was concentrated
3. C.When the concentrate was cooled, crystals formed were removed by filtration
4. D.The crystals were washed with very little cold water
5. E.The crystals were then allowed to dry.