6. why are ionic substances not known as molecules?

So, an ionic compound actually has two (or even more) different species in a single crystal or solution, which exist independently. The only reason why they are together is because of the total net charge, which must be zero.

ionic compounds are not known as molecules because they contain aggregate of positive and negative charges which arise from the transfer of electron from the metallic atom to the non-metallic atom. But in covalent substance, there is a sharing of electron pair between the atoms involved and this makes them to form a molecules

Explanation:

c is the answer because when something is left after something evaporates that shows the chemical change.