It has to be dilute since the crystal dissolved and unsaturated for the same reason so B
(99% of the total mass). 49% of carbon, 44% of oxygen, 6% of hydrogen, 0.1-0.3% of nitrogen.
You have to note that pure substances can be elements or compounds. There is only one component all throughout. On the other hand, a mixture is a combination of different elements and compounds. They can appear in different phases. For example, air is a mixture. It is composed of pure substances of oxygen, carbon dioxide, and nitrogen.
I would say the answer is C
