Examples of index fossils. Index fossils (also known as guide fossils, indicator fossils or zone fossils) are fossils used to define and identify geologic periods (or faunal stages).
Methyl cellulose. Methyl cellulose (or methylcellulose) is a chemical compound derived from cellulose. It is a hydrophilic white powder in pure form and dissolves in cold (but not in hot) water, forming a clear viscous solution or gel.
Solubility of a solid in water (without reaction) suggests it is ionic. There are exceptions to this, of course. Sugar (sucrose) is soluble in water despite being a covalent molecule. It is capable of extensive hydrogen bonding with water molecules. And there are a lot of ionic compounds which are insoluble in water, of course.